Cellular xenoresponses: Observation of significant primary indirect human T cell anti‐pig xenoresponses using co‐stimulator‐deficient or SLA class II‐negative porcine stimulators

We have documented the strength and characteristics of the in vitro human anti‐porcine indirect T cell response using porcine stimulators that were unable to provoke a direct xenoresponse. Our results indicate that HLA‐DR‐restricted and HLA‐DQ‐restricted CD4 + T cells recognise porcine xenoantigens presented by conventional APC, rather than xenospecific B cells. Limiting dilution analysis assays indicate a high precursor frequency of T cells with indirect xenospecificity in the peripheral blood of human responders. These data demonstrate that the indirect response requires no priming, but instead reflects the large number of pig‐specific antigens.