The Immunoregulatory Effects of Merocyanine 540 on In Vitro Human T- and B-Lymphocyte Functions

Merocyanine 540 (MC 540} is a photoactive dye used to purge bone marrow of tumor cells in autologous bone marrow transplantation. The effects of MC 540 on the lymphoid components in the marrow are unknown. This study evaluates the treatment of lymphocytes by MC 540 (15 μg/mL) and light (70 W/m2) on: (1) phytohemagglutinin and Con A-induced proliferation; (2) allogeneic mixed lymphocyte cultures (MLC); (3) the regulation of Ig synthesis by T cells; and (4) the ability of B cells to produce polyclonal Igs as measured by an enzyme-linked immunosorbent assay-plaque assay. The results show that MC 540 and light treatment reduced Con A-stimulated T-cell proliferation greater than 50% after 30 minutes and greater than 80% after 60 minutes of MC 540-sensitized photoirradiation. Ninety minutes of MC 540 and light exposure (designated treatment) inhibited MLC greater than 90%. In polyclonal Ig synthesis, T-cell helper activity could be abrogated by 90 minutes of treatment in cocultures containing untreated B cells. Purified B cells treated for 90 minutes cocultured with normal T cells did not produce Ig. Treatment of B cells completely inhibited Epstein- Barr virus-stimulated Ig synthesis. These data show that T- and B-cell immunity is suppressed by the MC 540-sensitized photoirradiation. Treatment of bone marrow with MC 540 and light may have profound effects on immune reconstitution in autologous marrow graft recipients. More provocative is the fact that the same immunomodulatory effects may be applicable to partially mismatched marrow transplant situations as a means of reducing graft-versus-host reactions.