Interleukin-2-producing helper T lymphocyte precursor frequency and rejection: a longitudinal cellular study after cardiac transplantation.

Interleukin-2-producing helper T lymphocyte precursors (HTLp) in the recipient recognize donor alloantigen expressed by the transplanted organ. The frequency of these reactive cells in the peripheral blood was determined and correlated with rejection episodes. Endomyocardial biopsy is generally used to quantify cardiac allograft rejection and guide immunotherapy. While non-invasive techniques have been investigated, none of these has demonstrated sufficient sensitivity or specificity to replace myocardial biopsy. Twelve cardiac transplant recipients were assessed over a 1 year period using limiting dilution analysis, to determine the frequency of HTLp in response to cadaver donor splenocytes. The IL-2-dependent mouse cell line CTLL-2 was used to measure the IL-2 present and the precursor frequency was calculated using maximum likelihood estimation. In the months immediately post transplantation, six of the 12 recipients displayed an association with increases in HTLp frequency, which preceded histologically detectable rejection. The second six recipients had fewer rejection episodes and achieved 'acceptance' of their graft sooner. Once 'acceptance' was achieved, the association between IL-2 HTLp frequency and rejection was no longer apparent. The ability to identify two groups of patients on the basis of IL-2 HTLp frequency clearly highlights the heterogenous nature of the response to the graft and this emphasizes the need to monitor other cytokines, which may influence the functioning of effector T cells.