De novo alloreactive memory CD8 + T cells develop following allogeneic challenge when CNI immunosuppression is delayed

• CNI initiation immediately post-challenge prevents memory CD8 + T cell development.
• Delaying CNI initiation post-challenge permits memory CD8 + T cell development.
• Memory CD8 + T cells develop when CNI is delayed to at least 6 days post-challenge.

Allospecific memory T cells are a recognized threat to the maintenance of solid-organ transplants. Limited information exists regarding the development of alloreactive memory T cells when post-transplant immunosuppression is present. The clinical practice of delaying calcineurin inhibitor (CNI) initiation post-transplant may permit the development of a de novo allospecific memory population. We investigated the development of de novo allospecific memory CD8 + T cells following the introduction of CNI immunosuppression in a murine model using allogeneic cell priming. Recipient mice alloprimed with splenocytes from fully mismatched donors received cyclosporine (CyA), initiated at 0, 2, 6, or 10 days post-prime. Splenocytes from recipients were analyzed by flow cytometry or enzyme-linked immunosorbent assay for evidence of memory cell formation. Memory and effector CD8 + T cell development was prevented when CyA was initiated at 0 day or 2 days post-prime (p < 0.001), but not 6 days post-prime. Following a boost challenge, these memory CD8 + T cells were capable of producing a similarly sized population of secondary effectors as recipients not treated with CyA (p > 0.05). Delaying CyA up to 6 days or later post-prime permits the development of functional de novo allospecific memory CD8 + T cells. The development of this potentially detrimental T cell population in patients could be prevented by starting CNI immunosuppression early post-transplant.