A notable phenomenon recapitulated. A fusion product of a murine lymphoma cell and a leukemia virus-neutralizing antibody-producer host plasma cell formed spontaneously and secreting the specific antibody continuously.

In the mid-1960s the #620 cell passage line of a murine lymphoma-leukemia was developed at the Section of Clinical Tumor Virology and Immunology, Department of Medicine, The University of Texas M.D. Anderson Hospital in Houston, TX. The diploid lymphoma cells released a retrovirus and were antigenic in young adult Swiss (YAS) mice. Small lymphoma cell inocula were rejected with immunity acquired against large inocula of lymphoma cells. Tissue sections revealed the "starry sky" configurations. In one of the tissue cultures set up from lymphoma #620, a cell line consisting of large round poly- or tetraploid cells arose and was referred to as lymphoma cell line #818. The #818 cells grew in suspension cultures and in the form of large, lethal ascitic tumors in YAS mice. Diploid #620 lymphoma cells stained for retroviral antigens; #818 cells stained both for retroviral antigens and immunoglobulins. Fluids withdrawn from #818 cultures neutralized the leukemia virus in spleen focus assays. Immunoglobulin precipitated from #818 suspension culture fluids strongly and specifically neutralized the leukemia virus. The growth of #620 or #818 cells in YAS mice treated with rabbit anti-lymphoma cell immune sera was strongly inhibited but culture fluids of #818 cells showed weak and insignificant inhibition against leukemia-lymphoma #620 (in one experiment, unpublished). In two experiments #620 lymphoma cells were co-inoculated with immune spleen cells into the peritoneal cavities of YAS mice. The immune spleen cells derived from mice that rejected #620 cell inocula or were actively immunized with a photodynamically inactivated mouse leukemia virus vaccine. In the peritoneal cavities of mice co-inoculated with #620 cells and immune spleen cells, clones of large round cells emerged with tetra- or polyploid chromosomal modes. These cells stained for leukemia viral antigens and immunoglobulins. When passaged in YAS mice these cells induced lethal ascites tumors. It was concluded as early as in 1968-69 that an immune plasma cell can fuse with a lymphoma cell, if the lymphoma cell expresses retroviral antigens against which the plasma cell is producing a specific antibody. Some human lymphoma-leukemia cells express retroviral antigens and/or budding retroviral particles, whether due to the acquisition of new env sequences by incomplete resident endogenous retroviral genomes or due to the entry of exogenous retroviruses into lymphopoietic stem cells. In the Discussion illustrations are provided for the human cell line #778 established from a patient with "lymphosarcoma cell leukemia" in 1966. The malignant cells released unidentified retrovirus-like particles and fused with one another and with reactive lymphoid cells of the host. It should be investigated further if human lymphoma-leukemia cells could fuse with an immune plasma cell of the host and thus alter the clinical course of the disease.