Thymosin-induced T cell marker expression and enhanced mitogen responsiveness in allogeneic marrow transplant recipients.

Thymosin fraction V, prepared from calf thymus glands was incubated with lymphoid cells from allogeneic bone marrow transplant recipients to determine the effects in vitro of thymosin on the expression of a T cell surface marker and on T mitogen-induced proliferative responses. Between 2 and 7 weeks after transplant, thymosin, after a brief coincubation, induced additional patient lymphoid cells to express the receptor for sheep erythrocytes. Between 1 and 8 months after transplant, thymosin, after an overnight preincubation, induced enhanced proliferative responses to phytohemagglutinin, concanavalin A, and occasionally pokeweed mitogen. These data suggest that marrow transplant patients had circulating lymphoid cells that were sensitive to thymosin, Thymosin induced the expression of a T cell receptor and enhanced the performance of a T cell functional response. Thymosin appeared to drive the maturation sequence of marrow transplant patient peripheral T cells. These studies were performed at a time when the allogeneic marrow transplant recipients were markedly immunodeficient and susceptible to opportunistic infections. These results suggest that thymosin fraction V may be useful to stimulate the immune system in vivo in patients after allogeneic marrow transplantation.