The object of this study was to examine the possibility of immunotherapy using anti-human immunodeficiency virus type 1 (HIV-1) p17-derivative peptide monoclonal antibody (MAb), namely MAb 8H10. Previously we established MAb 8H10, and further characterization revealed that it inhibited the viral multiplication of the HIV-l-infected MT-4 cells, and that the inhibitory mechanism related to the decrease of p17 DNA of the infected cells. In the present study, based on the assumption that Hybridoma 8H10 (Hyb 8H10) is a source of this MAb, we examined how Hyb 8H10 influences the infected cells when the two are co-cultured using the transwell or by mixed culture. Hyb 8H10 did not influence the cell growth or viability of MT-4 cells, and MAb 8H10 was transferred to the cluster dish containing the infected cells, Furthermore, Hyb 8H10 could produce MAb 8H10 even when co-cultured with the infected MT-4 cells. However, the infectivity of tbe supernatant of the infected cells was temporarily enhanced when Hyb 8H10 was co-cultured without MAb 8H10, though it gradually reduced according to the increase in MAb 8H10 produced by Hyb 8H10, Though there were some problems, MAB 8H10 proved to be a strong candidate for immunotherapy against HIV.