Cervical cancer (CC), is one of the most frequent cancers with one of the highest rates of death among women worldwide, it counts for nearly 10% of the total newly diagnosed cancer cases and 8% of the total cancer deaths [1]. The development of CC has generally been related to the presence of pathogens such as the human papillomavirus (HPV) as the principal etiological agent [2]. CC is frequently diagnosed in women between the ages of 35 and 65 (20% of cases of CC are found in women over 65) though it may silently commence at a very young age, even earlier than 20 years old [1,2].

Nevertheless, the immune system is able to take over the majority of HPV infections, with only a small percentage progressing to precancer and cervical changes as the majority of patients remain asymptomatic or show transient positivity [3-5]. In fact, as confirmed by recent outcomes, the HPV-only presence is not sufficient to explain the CC development and progression. Recent evidence showed that another agent needs to be there to increase the carcinogenic process, the outcomes showed the C trachomatis as the strongest co-infectious agent [3]. The data revealed that a high prevalence of C trachomatis infection was observed concomitantly with HPV-positive women (7-10%) than HPV-negative ones (>4%) in the presence of CC [3].

Either C trachomatis or HPV are common sexually transmitted infections (STIs) sharing structural traits, since both pathogens' DNA can be detected in around 99% of CC cases. However, whether both agents should be considered the ultimate risk for CC's insurgence would not completely explain the whole picture, especially if one considers the great diversity in time manifestation. The doubts are related to the infection "roller-coaster" mode which increases the need to investigate further factors eventually responsible for the process such as the role of local microbiota and the immunity status. Intriguingly, this position was formerly confirmed by a few studies that tested the effects of both HPV and C trachomatis infections on males diagnosed with chronic prostatitis in a presence of local dysbiosis [3-6]. The results obtained from urine specimens of both healthy and controls revealed that the microbiota differed according to different urologic diseases such as urinary incontinence, neurogenic bladder dysfunction, urologic chronic interstitial cystitis, and chronic nonbacterial prostatitis. Nowadays, we also know that alterations in the normal gut microbiome may affect the urinary tract, causing specific urologic diseases [7-9].

Interestingly, tissue alteration due to an unbalanced microbiota is not always related “the facto” to the presence of perilous microorganisms, as it was demonstrated it could be a consequence of the unappropriated use of antibiotics. The absence of any identifiable bacterial infection could be a distinctive feature of prostatitis, while an unnecessary use of antibiotics that alters the microbiota protective shield may be a precipitating factor, favoring the entry of opportunistic infectious agents [7,8].

This chicken-or-egg dilemma may add some confusion. Therefore, why can some individuals get through the infection without problems while others have difficulties in fighting it? Though there is a general agreement about immunity and hormones, little consensus remains on the role of microbiome an altered microbiota with dominant Lactobacillus iners over Lactobacillus crispatus with a concomitant decrease in Lactobacillus, Bifidobacterium, Enterobacter, Atopobium, and Streptococcus [9].

Those changes lead to considering carcinogenic mutation as a multistep process in which multiple factors are involved during a period of time. A scenario characterized by an overlapping condition in which pathogens' infected cells are going through DNA alterations that enable genetic and epigenetic events allowing viral replication and, setting the perfect stage for neoplastic changes [7-13].

These mutations take place concomitantly to changes in the expression of immune surveillance components and the system's homeostasis that have been shown to take place in response to oxidative stress. Important mutant transcriptomes are related to those genes regulating scavengers in the enzymatic defense against oxidizing agents that eventually damage proteins and nucleic acids, in particular, the expression of SOD2, CCP1, and CTT1 genes as they are involved during respiratory metabolism to limit high reactive species of the oxygen (ROS) production [12,13].

Furthermore, it has been shown that an immune-compromised microenvironment characterized by the presence of single nucleotide polymorphisms (SNPs) that may affect the expression of immune-modulatory cytokines (interferon gamma-IFN-γ, tissue growth factor beta-TGF-β, interleukin 10 and 1β), should also be considered congruent of an altered microbiota condition, as previously described, characterized by dominant Lactobacillus iners over Lactobacillus crispatus, Lactobacillus, Bifidobacterium, Enterobacter, Atopobium, and Streptococcus [7-10].

However, the peculiar trait of cancerous end-stage can only be possible via the persistent co-infection characterized by the concomitant presence of HPV and C trachomatis. According to some scientists, there is a mutual benefit between the two; while C trachomatis generate the convenient substratum leading to the permeability of the surrounding tissues allowing the HPV penetration into the epithelial cells, the HPV alters the immune detection allowing the C trachomatis to spread and multiply [3-5, 14-16].

In the presented paper we extended these findings that brought together different aspects that are sequentially involved in the CC etiology. We proposed an all-inclusive perspective, that includes the pathogens' role, genetic make-up, microbiota integrity, and immune responses, all patterns which we consider crucial in understanding CC pleiotropism. In this view, HPV and C trachomatis are seen as the players responsible to trigger chronic and recurrent infections procuring long-term inflammation of the genital area, altering local immune mediator's responses, increasing the production of ROS and free radical generation, causing tissue and cell damages promoting local degenerative mutations [fig.1,2].

2. The key role of local microbiota

The vaginal microbiota is a very dynamic ecosystem, and similar to the gut the local microbiota is composed of different strains with unique features and tissue interactions. The vaginal microenvironment is a densely populated area in which local bacteria perform a great variety of bio-activities under the guide of specific gene expression in charge of enzymes necessary for specific defenses and biotransformation [17,18]. In fact, patients affected by both colorectal cancer and CC showed lower levels of butyrate agent producers in the local microbiota than healthy individuals indicating an important shift in terms o local flora homeostasis [17-19].

The vagina and ectocervix microenvironments are characterized by the presence of specific lactic acid-producing bacteria capable of secreting a particular lubricant that traps invading pathogens [20]. The bacteria that make up the vaginal microbiome are inextricably linked to the acidity of the vaginal environment. The local flora is crucial for the local microbiome homeostasis, and the whole chain of bio-reaction takes place with a specific mean pH of 4 - 4.5. A vagina with a pH of 4.5 or below serves as a protective shield against harmful pathogens that are unable to survive in such an acidic environment. When pH is elevated (alkaline), harmful bacteria gain the opportunity to move in, disrupting the vaginal ecosystem [20-22].

Therefore, any changes in local balance homeostasis and in pH negatively may have a direct impact on the mucosa integrity that is functional to the outside and inside permeability gradient [21,22]. Once broken, the mucosa and tissues become an easy target of aggressive microorganisms and inflammatory processes accelerating the deterioration process of both the endothelial wall and microbiota shield enhancing the accumulation of pro-inflammatory endotoxins and long-term pathogens allocation (fig.3) [20 -22].

Figure 3. The bacteria that make up the vaginal microbiome are inextricably linked to the acidity of the vaginal environment. The local flora is crucial for the local microbiome homeostasis, and the whole chain of bio-reaction takes place in spaces with a specific mean pH of 4 - 4.5. A vagina with a pH of 4.5 or below defends against harmful pathogens that are unable to survive in such an acidic environment (C Gargiulo Isacco, K CD Nguyen).

Different results confirmed that the degree of severity of cervical neoplasm is linked to these local and systemic changes that negatively affect microbiota balance and functionality, especially against those health-associated strains like Lactobacillus spp. driving to an increase of anaerobic bacteria including Gardnerella spp, Prevotella spp., Atopobium vaginae and Sneathia spp., Megasphaera spp., and others [23]. Changes in the vaginal microbiota composition across cervical carcinogenesis may also lead to a profound switch into high pH with ROS elevation which is considered a general marker indicative of inflammation, abnormal apoptosis, angiogenesis, hormonal imbalance, metabolic dysregulation, suppressed local antitumor immunity and disease progression [23,24].

Both in vitro and in vivo models confirmed the effects of different Lactobacillus strains on both Chlamydia and HPV infection. It was found that L. iners, L. crispatus, L. jensenii, L. salivarius, L. gasseri, L. mucosae, and L. reuteri all significantly reduced C trachomatis infection in a dose- and time-dependent manner. The strongest anti-Chlamydia effects were linked with L. crispatus (90 percent reduction), whereas the poorest was found in L. iners (50 percent reduction). The d (–) lactic acid (LA) is crucial component in Lactobacillae cell-free supernatants able to inactivate either Chlamydia Ebs or HPV, showing a positive correlation with the anti-Chlamydia activity by neutralizing the pH value to 7.0 [24]. Outcomes from models inoculated intravaginally with Lactobacillus mixtures (L. crispatus, L. reuteri, and L. iners at a ratio of 1:1:1) following genital Chlamydia infection, confirmed this trend of decreasing its activity shedding in both the lower genital tract and the intestinal tract [24]. The beneficial effects are mostly seen in modulating the capacity of super reactive T cells, NK cells, and macrophages (M1) consequently reducing redounding cytokines production (TNF-α, IFN-γ, and IL-1β) in the vagina, and a diminished overall genital tract inflammation and pathogenicity [25,26].

Both L and D isomers of LA are strictly dependent on strains, with an active protonated form of LA predominating at pH below 3.9 [25]. Intriguingly, therapy using both isoforms of LA at pH 3.9 promoted better integrity of the barrier on ectocervical epithelial cells as compared to untreated cells (fig. 1), results that were not achieved with media acidified to the same pH with HCl. Nevertheless, a genital environment dominated by Lactobacillus spp. showed to keep a pathogen-free area and has been associated with optimal pregnancy outcomes [25,26].

3. The immune profile of CC microenvironment C trachomatis and HPV crosstalk

In the CC, a compromised microenvironment is mainly a consequence of deconstructed constituent parts of the vaginal microenvironment [26,27]. The intrinsic problems recall the simultaneous presence of multiple factors such as the high inflammatory state, the presence of SNPs on genes regulating the expression of immunosuppressive cytokines and interleukins, and a persistent local dysbiosis that in turn facilitate the long-term aggressiveness of the HPV and Chlamydia infection [19,28]. The outcomes on the female genital tract either at vaginal or cervical microbiota together with a substantial cytokine profile have identified changes in microbiota diversity among women affected by HPV and C trachomatis infection, with bacteria/viral vaginosis (BVV) [28-31]. The co-infection with C trachomatis and HPV (especially the 16,18, 31,33, 53, and 56 genotypes) has been considered the most important risk factor for the presence of CC, especially in young, unmarried women who started their sex lives early with several sexual partners and who used oral contraceptives [14-16,22]. Interestingly from these studies, it comes out that the prevalence of C trachomatis was high predominantly in young women [14-16].

The immune response to acute HPV infections is initially mediated by mucosal NK cells, macrophages (M1 in the acute phase and M2 in the reparative phase), and epithelial cells which produce antimicrobial peptides with known anti-viral/bactericidal effects. Since HPVs have evolved molecular strategies to escape innate and adaptive immunity barely seen inflammatory patterns while the infection is often marked with a rather high number of CD4+ CD25+ regulatory T cells and the presence of activated TH2 cells with the suppression of cytotoxic functions that drive to T cell anergy, a condition that may explain the increased rate of co-infective patterns due to other sexually transmitted diseases pathogens such as C trachomatis [28,32].

A few important HPV genotypes, such as the16 genotype, showed the capacity to interact with C trachomatis development generating a sort of C trachomatis steady persistence [31,32]. At this point many authors described the deep interchangeable behavior between the two pathogens; at transcriptional and post-translational levels both HPV and C trachomatis interfere within the host's cells reprogramming mechanisms that subvert the self-repair mechanisms [31,32]. The sabotage also involves the stem cell cloning mechanism reducing the local regenerative capacity leading to an increase in tissue damaging [31,32].

Of note, the intracellular life of C trachomatis is characterized by a vacuole surrounded by a membrane, called “inclusion”, in which it replicates followed by the transition from EB to RB and back to EB, the final form ready to exit the cell and infect other cells [3-5]. By this moment, C trachomatis start triggering the activation of the oncogenic pathway of Ras-Raf-MEK-ERK with the production of ROS to create the ideal microenvironment to support cancer cell growth [4,5]. The mechanism is mostly based on C trachomatis ability to create mitotic spindle defects by aborting the spindle assembly checkpoint (SAC) causing the host cell to prematurely exit mitosis without the right corrections [30-34]. Nonetheless, C trachomatis tend to subvert the host's histones, triggering the upregulation of PH2AX and H3K9me3, both hallmarks of DNA double-stranded breaks (DSBs) and senescence-associated heterochromatin foci (SAHF) [30-34].

It's confirmed that supernumerary centrosomes have been identified in several types of carcinomas, as either addition or subtraction of chromosomes due to mitotic defects and can reasonably be considered a sign of tumor growth and progression [30-34]. As previously mentioned the increased ratio of ROS also contributes to DSBs that in turn elicit SAHF formation in an ERK-dependent manner. It should be mentioned that C trachomatis is capable of blocking the use of DNA damage response (DDR) proteins such as pATM and 53BP1, despite these cells keep conserving their proliferative ability supported by oncogenic signals involving ERK, Cyclin E, and SAHF [34,35]. Furthermore, both HPV and C trachomatis can also act at post-transcriptional and post-translational levels interfering with those genes controlled by an E2F transcription factor and associated with the DNA mismatch repair (MMR) mechanism [30-35].

Therefore, we assume that the possible correlation between C trachomatis and HPV coinfection with cervical tissue changes could be based on the steady though the active presence of both pathogens that pervasively and silently keep subverting the host's detection and repairing mechanisms at a very molecular level which explain the reason why the large percentage of affected women remain asymptomatic over a long period of time [33-36].

As a predictive tool of possible CC high risk among those females with tubal infertility and asymptomatic it could be of help in assessing the vaginal microbiota condition and the local immune expression in the presence of both HPV and C trachomatis. As matter of fact, no significant differences in phylum, class, and operational taxonomic unit (OTU) levels were observed among women with tubal infertility who were C trachomatis negative and healthy controls [35].

4. The crosstalk between microbiota and the immune-endocrine system

Similarly to the intestines, vaginal microbiome composition is not equally expressed over the female reproductive tract. Lactobacillus spp appears to be the majority in the uterus, the non-Lactobacillus spp are major parts of the uterine cervix while the vagina is normally predominated by Lactobacillus spp of the Community State Types (CST) I, II, III, and V. The CST-IV is composed by a polymicrobial mixture of anaerobes suggesting that any predominance of CST-IV is clinically related to bacterial vaginosis [37]. It is well accepted that innate immune responses are driven by vaginal bacterial community conditions, the CST-IV plays a potential role in scattering the higher pro-inflammatory responses compared to others [37].

Not only does the vaginal microbiome is able to produce hormones, but it can also communicate to the endocrine glands how much of each hormone is needed. However, this relationship is bidirectional since the host-bacterium interaction also depends on sex and hormones via interactions among its metabolites, the immune system, chronic inflammation, and nerve-endocrine/paracrine pathways [38]. Data showed early childhood microbial exposures would play a key role in setting up sex hormone levels which in turn determine the typology of immune responses. Several attempts in microbiota transplantation in animal models from adult male mice to immature female mice lead to a hormone level modification with an increase in testosterone level and metabolomic changes in autoantibody production [38].

For instance, the results from a study by Yurkovetskiy and colleagues showed that sequenced bacterial DNA extracted from the caecal contents of prepubescent mice (4 weeks old) and postpubescent mice (10–13weeks old), the α-diversity was not significantly different between the two sexes in prepubescent mice. Conversely, it was observed a gender bias like those among postpubescent mice. Once sequenced 16S rRNA genes were from the microbiota of male, female, and castrated male, the outcomes confirmed something “unusual”, the microbiome of females was highly similar to that obtained from the castrated males reflecting the similar composition and levels of androgen hormones [39].

In the same way, samples obtained during the pregnancy period showed that vaginal microbiota composition tends to modify reflecting the changes in hormones level and typology. It was observed an increase in phylum Firmicutes from Trimester I to Trimester III, which characterizes the vaginal microbiota of healthy women [40]. Conversely, dysbiosis of vaginal microbiota during BV has been reported to be characterized by diverse bacterial taxa belonging to specific phyla such as Fusobacteriota, Actinomytetota, Pseudomonodota, and Bacteroidota [41]. Similarly, the vaginal microbiota of pre and peri-menopausal women are mainly composed of phylum Firmicutes the vaginal microbiota in post-menopausal women confirmed to harbor mainly phyla, Proteobacteria, Bacteroidetes, and Actinobacteria [40,41].

However, a key fact is a deep relation between the different components of the genital area based on the presence of specific receptors. Recognition cell receptors are located everywhere either on squamous epithelial cells of the vagina or on the columnar cells lining the upper female genital tract capable of recognizing bacterial products expressed by the vaginal microbiome [42,43]. Of course, the vagina, endometrium, and tubes are equipped with high-functioning immune cells and androgen receptors which completely synchronize with the microbial environment. The interplay between the immune system and the microbiome involves hormone receptors together with different immune mediators, stem cells, leukocyte subsets, plasma cells, IgG , IgM, and IgA antibodies, interleukins, and inflammatory proteins [42,43]. Lactobacilli play a pivotal role capable of modulating both inflammatory and anti-inflammatory responses directly modulating local production of interleukins IL-1β, IL-6, and IL-8 and IL-2, IL-10, IL-173 [42,43] (fig.4).

Figure 4. the Eubiosis of female sex apparatus is based on the balance of several factors composed by microbiota, hormones, local bacteria which is then associated to regular and equilibrated immune responses, diet and active life style.

Immunologically, hormones play a fundamental role as they actively participate in regulating the production of antimicrobial peptides (β α-defensins, SLPI) and pro-inflammatory cytokines expressed by local epithelial cells especially in ensuring the safety of sperm and preventing infections [37]. Estrogens are the major contributors to microbial populations selection during the different aging phases, for instance in prepubertal age, vaginal microbiota is mainly characterized by anaerobic species of the Enterobacteriaceae and/or Staphylococcaee family; in puberty, the estrogens promote the accumulation of glycogen by mature epithelial cells [37-39]. The presence of both maltotriose and alpha-dextrins, derived from glycogen digestion is an extremely important food for Lactobacillus species and their production of LA [38,39].

It clearly comes out that the microbiota system, immune and endocrine systems are part of a unique hyper-specialized unit that ensures vital functions in the body, organizing and performing crucial activities. Microbiota and immunity cooperate to protect from lethal pathogens, whereas the microbiota and endocrine system ensure the proper metabolic function of peripheral organs by regulating systemic homeostasis. In this view, the cross-talk between microbiota, hormones, and immune system cells could be seen as a further point in understanding vaginal infections and aggressive pathogens that may lead to carcinogenesis [42-47].

5. Modern diet and lactobacillus issues

The balance of the vaginal microbiome is constantly influenced by various local and systemic factors, such as diet, hormonal levels, smoking, and the use of topical products or antibiotics. Aging plays a deep role in vaginal microbiota composition and vaginal physiology is modified by vaginal microbiota composition [46-48]. During pregnancy, the first microbial colonization occurs at the time of the delivery supplied by the mother's vagina or skin, depending on the route of birth. In female newborns, both the vulva and vagina are affected by the presence of transplacental estrogenic residues allowing glycogen supply and then metabolized by endogenous bacteria, lowering the vaginal pH [49]. As estrogens are metabolized, vaginal glycogen content is lost switching towards an alkalized pH which is neutral up to puberty. During puberty, the maturation of adrenal glands and gonads induces a rising in the levels of estrogens as well the intracellularly. Two main types of colonies have been determined at this stage the Lactobacillus spp. and Atopobium and Streptococcus spp [49].

However, age-related microbiota changes (dysbiosis) contribute to inflammation because long-term stimulation causes immune-senescence rendering the host more sensitive to potentially harmful bacteria which in turn contributes to the higher rate of different pathological conditions in the elderly [39-41 ].

According to the dietary outlook in this small review, we can refer to "Healthy diet style" and "Unhealthy diet style". The modern industrialized "Unhealthy diet" habits are defined by high loading of sugar, solid oils, highly refined carbohydrates and refined grains, fried potatoes, and sweet drinks and, have been substantially associated with higher BVV odds [45-50]. For instance, overweight women are more prone to have higher rates of infections either bacterial or viral compared to lean women, thanks to different mechanisms including alterations in hormonal, metabolic, or immunological functions which tend to affect the overall structural stability of vaginal microbiota. For instance, high glycogen levels following high starch intake there was seen in an altered condition of the composition of the genital fluids [41,42].

A higher risk of molecular BVV was seen in women with low vitamin D, A, E, β-carotene, and iron, the results were assessed by using 16S rRNA gene amplicon sequencing [43,44]. Interestingly, it has been proposed that the impact of certain micronutrients on the vaginal microbiota could be mediated through the effects on the gut microbiota. Of note, several studies have noted concordance between rectal and vaginal carriage of specific bacteria, including Lactobacillus spp. With a decreased risk of BVV [43,44,50]. Experiments performed on rats and pigs assessed via qPCR showed that high levels of vitamin D, A, E, β-carotene and iron supplementation improved the function of digestive enzymes and increased the relative abundance of the genus Lactobacillus in the gut microbiota [41-44 ,50]. Among these micronutrients, vitamin D attracted great attention. Outcomes reported serum level of 25-hydroxy-vitamin D [25(OH)D] as negatively correlated with BVV in pregnant women during the first trimester validated by different studies that associated the low level of D and BVV during pregnancy probably via the existing correlation between Lactobacillus crispatus and serum 25(OH)D [46,47]. Although, it is unclear how applicable animal data may be to humans for the use of enteric bacteria can deconjugate estrogens and promote their reabsorption to the circulatory system leading to glycogen and mucus production and thickening of the epithelium of the lower genital tract. Thus, a reduction in estrogen-metabolizing bacteria could influence the Lactobacillus dominance in vaginal flora [46,47].

In addition, a high carbohydrate and fat intake induces are known to induce dysbiosis via the down-expression of angiopoietin-like protein 4 (Angptl4) resulting in lipoprotein lipase (LPL) hyperactivity. The elevated LPL has direct consequences on higher uptake of fatty acids which in turn increases fat accumulation in peripheral tissues and thus inflammation [48].

The Bifidobacterium spp., Lactobacillus spp., and Prevotella spp. are known to be highly sensitive to fat and refined sugars which affects their role in the activation and modulation of the endocannabinoid system. These changes contribute to altering the gut microbial composition generating the phenomenon known as “ The leaky gut” allowing bacteria translocation within and in-out the gut compartments. Furthermore, this typology of foods has shown a direct impact on Gram-negative pathogen's overgrowth and migration with bacterial fragments such as lipopolysaccharides (LPS) freely moving across the intestinal lumen, triggering the nuclear factor kappa B (NF-κB) pathway in the bloodstream which in turn open up the Toll-like receptors towards the activation of proinflammatory cytokine CD14, causing an increased intestinal permeability [48].

Smokers have also shown some clear predisposition towards infection by C trachomatis and HPV and CC insurgences. Data analysis found two shreds of evidence: (i) it was significantly more likely that smokers' vaginal microbiota had a low Lactobacillus prevalence and; (ii) metabolites produced during heat combustion were increased in higher Nugent scores [48]. Smokers and non-smokers were studied and compared, results showed differences in vaginal metabolites. Among these women biogenic amines were higher in smokers; these amines showed to have some sort of effect on the virulence of infectious pathogens contributing to vaginal malodor [52].

Stress also has the potential of threatening the balance, and homeostasis, of a vagina's internal background [25]. Trauma and negative emotions unfavorably affect the individual's sense of stability and depressed immune responses, outcomes from animal models reported that persistent exposure to psychosocial stress can lead to an encouragement of the hypothalamic–pituitary–adrenal–medullary axes (HPA) which drive a cortisol- induced inhibition of glycogen deposition in the vagina, ending with an interruption of epithelial maturation crucial to keep vaginal homeostasis [25]. This is a phenomenon particularly important during pregnancy, in which the high local production of corticotropin-releasing hormone occurs in the decidua, fetal membranes and placenta tending to compromise the fragile equilibrium between estrogen and lactobacilli activity and vaginal homeostasis [49,52,53,54].

6. New strategies and approaches in clinic

As far as we know, intestinal and vaginal tissues share many features both physiologically and pathologically including an immune system to protect from pathogen invasion and maintain homeostasis [54-57]. The great diversity of microorganisms composed of bacterial, archaeal, eukaryotic, and the dominant lactobacilli in the vaginal tract are strongly influenced by several factors including host genetic make-up, host bionomy, and environmental factors [54-57].

Though the probiotic approach showed some positive results so far, results still remain uncertain with nothing particularly definitive about its efficacy, therefore new strategies have been adopted showing very new potential [58]. The idea was simple and adopted the basic concept of organ transplant, using the fluid from a healthy vagina and transplanting it into an unhealthy one. In this case, behind it is all about bacteria since each individual practically carries trillions of bacteria living on and in their body, different strains, located in different locations performing different activities [56-58].

In the vagina, it seems that the complexity follows a precise homeostasis regulated by the presence of the Lactobacillus crispatus and hormones such as estrogen, progesterone, and testosterone. The limitation of exogenous probiotics therapy it's probably due to the fact that Lactobacillus crispatus and kindreds are not the same lactobacilli in dairy products nor the ones found in the gut [55,56]. The outcomes from a genomic study performed on Lactobacillus crispatus revealed that 37 strains had genes encoding 33 glycoside hydrolases (GHs) families. The level of GH1, GH13_18, GH2, GH20, GH25, GH3, GH36, GH43_14, GH73, GH78, and GH92 differed significantly (p < 0.05) between those obtained and analyzed from the gut from those from the vagina. Lactobacillus crispatus strains of gut origin contained more types of carbohydrate enzyme than the same strain from the vagina [55,56].

In addition, with a lower pH compared gut which helps to reduce the risk of gynecological infectious diseases and maintain local health and homeostasis, the local Lactobacillus crispatus evolved to face the harshness of acidity [50]. The vagina Lactobacillus crispatus expresses the gene encoding manganese transport protein takes up Mn2+ able by this way to expel protons out of the cell participating in the acid response, and maintaining intracellular pH homeostasis. The Mn2+ it's also an important tool that also helps in protecting Lactobacillus crispatus against oxidative stress [55-57].

Therefore, under a similar genetic background, the possibility of microbiome transplantation (VMT) gives a valid alternative model based on the role of the entire microbiota in the host defense mechanism [58]. At the moment there have been several exploratory studies testing the use of VMT from healthy donors as a new alternative therapy for patients suffering from symptomatic, incurable recurrent bacterial/viral vaginal infection. The concept follows the positive results obtained by fecal microbiota transplantation (FMT) successes for recurrent infections due to destructive bacteria and long-term inflammatory state (Clostridioides difficile and ulcerative colitis) [57,58].

However, the VMT varies and is not a one-size-fits-all procedure. The application may differ from person to person with a single procedure treatment to multiple top-up transplants. This indicates that compatibility requires considering variables, such as the species in the donor sample, the recipient's baseline vaginal environment, or both, in order to reach a proper match for the treatment to be effective, to ensure that no pathogens of foreign bodies (sperm ) could be transferred to the recipient. Sequencing the donor's and recipient's genetic patterns and microbes throughout will help to better assess the types of organisms that can establish themselves and thrive in each recipient, how the different communities vary based on the recipient's vaginal status, and the specific traits of dysbiosis and local pathological condition, such as endometriosis [60,61].

The therapeutic effects found that VMT showed an almost consistent inhibitory effect on both inflammations (lowering cytokines and downregulating the NF-kB pathway) and ectopic lesion progression effect in mice, indicating that vaginal bacteria may play an important role in endometriotic lesion progression and reconstructing the vaginal microbiota microenvironment to normal [60,61].

In conclusion, overall results confirmed that vaginal microbiota works as an antipathogen solid screen reducing the progression of inflammation, and endometriosis and eventually limiting carcinogenesis progression. A healthy microbiota and eventually the VMT approach have shown great benefits also in the treatment strategy for several gynecological diseases [60,61].

7. Conclusions

The risk of CC is a multifactorial matter, involving different factors and variants. The HPV-C trachomatis DNA host integration is usually a necessary event in the pathogenesis of HPV-C trachomatis related cancer; however, the mechanism of reciprocal validation and integration needs probably years and takes place in specific microenvironment conditions. In addition, one has to consider that any breaks or damage in the local immune surveillance must be also facilitated by either genetics or epigenetics factors for the integration occurs. In this regard, studies have shown that viral-bacteria integration is indeed eased by local dysbiosis which in turn increases pathogens' indiscriminate invasion and persistent inflammatory state. Furthermore, aging, (hormones unbalances) and diet also showed have detrimental effects contributing to inflammation raise and ROS uncontrolled persistence. Together these heterogeneous factors lead to host cells' DNA strand breaks enabling a stronger HPV - C trachomatis reciprocal integration. Consistent with this assumption, the silent long-term HPV - C trachomatis co-infections become the essential contributors to tissue transformation which drives to final CC. The prevalence of co-infection of C trachomatis and HPV is therefore an important contributory fact that may begin at a young age and silently persist as long as the vaginal microbiota, immunity, and hormones keep preserving local homeostasis. Obviously, microbiological screening and the vaginal test still remain the most effective diagnostic tools. Meanwhile, the future of microbiota-based therapeutics shall be performed on well-defined groups of microorganisms characterizing their specific beneficial effects on the host and the recipients. Therefore, precise identification of the microbial community members in either health or in dysbiosis should be the strong theoretical foundation of future prospective research that need to focus on the interactions between the microbiome and the host's immunity as well as the interactions between age, sex, the genetic predisposition and the underlying daily habits and diet behavior in both healthy and patients. This approach will certainly raise the rate of protection against pelvic inflammatory disease and infertility, and potentially will be of great help in preventing and reducing the incidence of CC.