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.