Functional studies on T cells in adult human bone marrow.

Bone marrow (BM) lymphocytes were obtained by sucrose density gradient centrifugation of the nucleated cells from adult human BM. BM was obtained from rib sections removed routinely during thoracotomy from thirteen patients with a localized lung tumour and from two other patients without tumour (mean age 47 years). The percentage of T cells in BM was high (mean +/- s.d. 27% +/- 17) and increased with age. In eight cases, the function of isolated BM T cells was studied and compared to that of peripheral blood (PB) T cells. BM t cells showed poor helper activity for pokeweed mitogen (PWM) induced Ig production by PB non-T cells, which did not appear to be due to excessive suppressor cell activity. Phytohaemagglutinin (PHA) induced thymidine incorporation was only slightly decreased but peak values were only reached after 6 years, in contrast to 4 days for PB T cells. This delay did not seem to be due to a lack of monocytes. PHA, however, failed to induce cytotoxic activity in BM T cells. PWM-induced thymidine incorporation and responder capacity in the mixed lymphocyte reaction were also very poor. These results are interpreted as suggesting that many of the T cells in adult human marrow are immature.