The effect of experimental conditions on the assessment of T cell immunomodulation by biological response modifiers (thymosin fraction five).

The coculture of spleen cells with specific antigens in the presence of thymosin fraction five (F5) results in the stimulation of the lymphocyte response. To observe the stimulation, a suboptimal responder-to-stimulator ratio must be utilized. Suboptimal assay conditions also are needed in immunization challenge studies in which thymosin F5 acts as an effective immunoadjuvant. The data reported here suggest that to study the efficiency of a biological response modifier, suboptimal assay conditions are best for observation of immunomodulation. We also report that thymosin F5, in addition to exhibiting adjuvantlike activity for T cells, is stimulatory in assays of mixed lymphocyte response and in the in vitro stimulation of cytotoxic T effector cells, following a mixed lymphocyte-tumor culture.