Recent studies show that costimulation of T cells with anti-CD28 Mab (anti-CD28) enhances anti-CD3 Mab (anti-CD3)-induced proliferative responses and cytokine production. This study determines if coactivation with anti-CD3 and anti-CD28 corrects defects in proliferation and IL-2 secretion in peripheral blood lymphocytes (PBL) from bone marrow transplant (BMT) recipients. PBL or T cells from 5 of 16 autologous and 5 of 22 allogeneic recipients increased their anti-CD3-induced proliferation responses by > 50% after coactivation. In short-term (< 180 days after BMT) autologous recipients, the group mean response increased after anti-CD3 activation from 62,900 to 97,800 cpm after coactivation. In long-term (> 180 day after BMT) autologous recipients, the group mean response after anti-CD3 activation increased from 62,600 to 78,400 cpm after coactivation. The long-term autologous recipient group had costimulated responses from PBL that were significantly higher than the paired anti-CD3-induced responses (p < 0.01); in contrast, such differences were not seen in allogeneic recipient groups. After anti-CD3 stimulation, the mean response of 88,000 cpm for PBL from short-term allogeneic recipients and the mean response of 83,600 cpm for PBL from long-term allogeneic recipients were higher than those in PBL from autologous recipients were higher than those in PBL from autologous recipient groups. The amount of IL-2 secreted by T cells from three autologous and three allogeneic recipients was enhanced 0.9-25-fold by coactivation. Coactivation of PBL from selected recipients increased proliferation into the normal range and increased IL-2 secretion.(ABSTRACT TRUNCATED AT 250 WORDS)