CD34⁺ cell proliferation stimulated by allogeneic T cells. Freshly isolated CB CD34⁺ cells were mixed with or without 5 × 104 irradiated autologous T cells (auto-T cells) or HLA-mismatched PB T cells (allo-T cells) at 1:2 S/R ratio, or medium, and cell proliferation was measured by 3H-Thymidine incorporation assay after 6 days of culture. Results are represented as the mean cpm ± SD of 3 separate experiments. (A) CD34⁺ cell proliferation was greater after coculture with allogeneic T cells than with autologous T cells or with medium alone (P = .02). (B) When anti-HLA class I (anti-class I) or anti-HLA class II (anti-class II) mAbs were added to the culture, only anti-class II reduced proliferation. Results are represented as the mean cpm ± SD of 3 separate experiments. Only the anti-HLA class II antibody reduced the CD34⁺ cell proliferation significantly (P = .04). (C) Addition of anti-TNFα (anti-TNF) and anti-GM-CSF (anti-GM) mAbs, or anti-TNFα mAb alone (P = .01), reduced proliferation in 3 separate experiments. ^*P < .05.