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Identifying new Markers and Homing Profiles involved in Lymphocyte Migration to the Female Reproductive Tract

Final Report Summary - FRT-HOMING (Identifying new Markers and Homing Profiles involved in Lymphocyte Migration to the Female Reproductive Tract)

The effort to develop vaccines that can elicit mucosal immune responses in the female reproductive tract (FRT) against sexually transmitted infections (STI) have been hampered by an inability to accurately measure immune responses in the genital tract. Vaccines against STIs should generate localized memory immune responses at sites of potential exposure to provide better control of infection. Limited access to mucosal tissues in women has hindered progress and revealed a critical gap in this area of knowledge. In the case of the female genital tract immune responses, assays to determine the magnitude and quality of the immune response in mucosal tissues largely rely on sampling of peripheral blood. Measuring antigen-specific T cell responses directly is not always technically or economically feasible, therefore methods that provide an indirect measure of the immune response are essential.

To this aim we worked on defining the homing profile of lymphocytes migrating to the female genital. Adhesion molecules expressed on effector T cells during genital tract infection could become excellent surrogate markers of genital tract immunity because of their accessibility and feasibility. This project was built on the hypothesis that lymphocytes induced by FRT immunization/infection traffic transiently in blood expressing a specific set of homing markers, but are selectively retained in the FRT after transmigration. The main goal was to identify specific integrins and homing receptors expressed on circulating lymphocytes that direct their migration to the female reproductive tract during the brief period in which mucosal lymphocytes re-circulate. To achieve this goal we proposed to isolate cells from blood shortly after mucosal FRT immunization/infection in animal models and patients, in order to identify proteins and gene transcripts potentially associated to T lymphocyte homing to the FRT.

Initial work on a mouse model of vaginal infection with Chlamydia provided specific candidate chemokine receptors and integrin chains significantly up-regulated compared to control mice. Preferential protein expression of these candidates, namely CCR2, CCR5, CXCR6 and CD11c, was confirmed in the same model at several time points after vaginal infection. We then addressed these and other adhesion molecules of interest in women with different peripheral tissue conditions, including bacterial vaginosis. Expression of CCR5 and CD11c was clearly increased in effector T cells during bacterial vaginosis (BV) in women, but not during other skin or gut inflammatory conditions. Other homing molecules previously suggested as required for homing to the genital mucosa such as a4b1 and a4b7 were also differentially expressed in these patients. Although we acknowledge the limitation of the sample size for the cohorts included in the study, the present results represent a unique comparison between peripheral tissue alterations that provide adhesion molecules of interest for each of the different disorders to further explore. However, CD11c expression, an integrin chain rarely analyzed in the context of T cell immunity, was the most consistently elevated in all activated effector CD8+ T cell subsets analyzed after intravaginal Chlamydia infection in mice and symptomatic BV in women.

CD11c is an alpha integrin classically employed to define myeloid dendritic cells. Although there is little information about CD11c expression on human T cells, mouse models have shown an association of CD11c expression with functionally relevant T cell subsets. This molecule was also induced after systemic Chlamydia infection in mice, suggesting that CD11c is not exclusive of genital tract infection. On the other hand, microarray analyses of activated effector T cells expressing CD11c derived from naïve mice demonstrated enrichment for natural killer (NK) associated genes. In fact, murine CD11c+ T cells analyzed by flow cytometry display markers associated with non-conventional T cell subsets, including gdT cells and invariant natural killer T (iNKT) cells. However, in women, only gdT cells and CD8+ T cells were enriched within the CD11c fraction of blood and cervical tissue. These CD11c+ cells were highly activated and had greater interferon (IFN)-gamma secretory capacity than CD11c- T cells. Furthermore, circulating CD11c+ T cells were associated with the expression of multiple adhesion molecules in women, suggesting that these cells have high tissue homing potential. These data suggest that CD11c expression distinguishes a population of circulating T cells during bacterial infection with innate capacity and mucosal homing potential.

Considering all the above, measuring T cells expressing CD11c in blood could be an indicator of T cell immunity directed to tissues of difficult access, such as the female genital tract. In this sense, preliminary data demonstrates expansion of gdT cells expressing CD11c during BV also in women. Additionally, if T cell subsets expressing this molecule are indeed protective, it would be desirable to induce this type of cells in the context of sexually transmitted disease vaccine development. Defining the role and clinical value of this biomarker in the context of female genital tract infections is a promising new tool that will certainly aid in the search of an effective vaccine, and research towards this goal is warranted.

STI represent a significant social, health and economic burden worldwide. We need to increase our efforts to assess mucosal responses in our search for correlates of protection during both preclinical and clinical evaluation of STI vaccine candidates. Results from our proposal define adhesion molecules, namely CCR5, a4b1 and CD11c, which may be desirable to induce in order to generate an effective mucosal response in vaccine candidates against STI. Special attention should be given to CD11c as a novel surrogate marker of T cell mucosal immunity in response to genital tract disorders in women. Our results provide not only a molecule associated to female genital tract homing, but also a novel therapeutic target to manipulate in the context of STI vaccines development, positively improving conditions affecting maternal and neonatal health.