T cell‐intrinsic PKD3 fine‐tunes differentiation into CD8+ central memory T cells and CD8 single positive thymocyte development

Members of the Protein kinases D (PKD) family are described as regulators of T cell responses. From the two T cell‐expressed isoforms PKD2 and PKD3, so far mainly the former was thoroughly investigated and is well understood. Recently, we have investigated also PKD3 using conventional as well as conditional T cell‐specific knockout models. These studies suggested PKD3 to be a T cell‐extrinsic regulator of the cells' fate. However, these former model systems did not take into account possible redundancies with the highly homologous PKD2. To overcome this issue and thus properly unravel PKD3's T cell‐intrinsic functions, here we additionally used a mouse model overexpressing a constitutively active isoform of PKD3 specifically in the T cell compartment. These transgenic mice showed a slightly higher proportion of central memory T cells in secondary lymphoid organs and blood. This effect could not be explained via differences upon polyclonal stimulation in vitro, however, may be connected to the observed developmental aberrances in the CD8 single positive compartment during thymic development. Lastly, the observed alterations in the CD8+ T cell compartment did not impact proper immune response upon immunization with ovalbumin or in a subcutaneous tumour model suggesting only a small to absent biological relevance. Taking together the knowledge of all our published studies on PKD3 in the T cell compartment, we now conclude that T cell‐intrinsic PKD3 is a fine‐tuner of central memory T cell as well as CD8 single positive thymocyte development. The role of Protein Kinase D3 (PKD3) in T cells is hitherto only incompletely understood. With a novel approach using mice overexpressing a constitutively active isoform of PKD3 selectively in T cells, we observed that this kinase (1) modulates CD8 single positive thymocyte maturation, (2) is dispensable for T cell receptor‐mediated activation, but (3) fine‐tunes the development of CD8+ central memory T cells.