Intrinsic and Extrinsic factors regulating competition for active TGFb promote skin memory CD8 T cell fitness

Abstract Resident memory T cells (Trm) are a recently appreciated subset of memory T cells that maintain long-term residence in barrier tissues. Unlike central memory T cells that reside in the lymph node and spleen, Trm are prepositioned at the site of a prior infection/inflammation where they provide a rapid immune response to subsequent challenges. In the skin, CD8+ Trm reside primarily in the epidermis and provide protective memory responses to herpes simplex and vaccinia virus infections that exceeds the protection provided by central memory T cells. In addition, epidermal Trm provide immune-surveillance against melanoma and are likely pathogenic in many autoimmune diseases. Understanding the basic biology of these cells is central to efforts to maximize barrier host defense and treat numerous diseases. In past cycles of the grant we showed that persistence of CD8+ Trm in the epidermis requires autocrine TGFβ that must be transactivated by avβ6 or avβ8 expressed by keratinocytes. We also found that partial blockade of avβ6 and avβ8 by mAb or small molecule inhibition could eliminate epidermal Trm. Importantly, only Trm that had not re-encountered cognate antigen in the skin were depleted. In contrast, Trm that re-encountered cognate antigen in the skin were able to persist when levels of active TGFβ were artificially suppressed. Thus, a second encounter with cognate antigen in the skin during development renders Trm less dependent on active TGFβ and represents a mechanism to preferentially deplete ‘bystander’ Trm during subsequent rounds of infection/inflammation. Moreover, TCR ligation during development in the skin promotes Trm ‘fitness’ and is an unappreciated obligate final step in the development of robust epidermal Trm. In Aim 1, we will test the hypothesis that TCR-induced alteration of the chromatin state is a key determinant of Trm ‘fitness’. We hypothesize that the niche size is flexible and that expression levels of avβ6 by keratinocytes is a key T cell-extrinsic factor determining its size. In Aim 2, we will develop mice with doxycycline controllable Itgb6 expression and test our hypothesis by directly manipulating αvβ6 expression at varying times following Trm development. Finally, we hypothesize that both T cell ‘fitness’ and TGFβ transactivation by the niche participate to shape antigen-specific CD8+ T cell pools in the context of chronic antigen. In Aim 3, we will test this hypothesis using a transplantable B16 melanoma model in which T cell ‘fitness’ and stromal TGFβ transactivation will be manipulated.