Combined Use of Dendritic Cells Enhances Specific Antileukemia Immunity by Leukemia Cell-Derived Heat Shock Protein 70 in a Mouse Model with Minimal Residual Leukemia Cells

Abstract

We have reported that immunotherapy using leukemia cell-derived heat shock proteins (HSPs) is effective against minimal residual disease (MRD) after syngeneic stem cell transplantation (SCT) in mice. However, leukemia patients after SCT are usually immunocompromised and immunologically tolerant to leukemia cells. We investigated whether the use of dendritic cells (DCs) in combination with HSP70 enhances cytotoxicity against B-cell leukemia cell line A20 in mice after syngeneic SCT. All unimmunized mice died of leukemia early after A20 cell inoculation, whereas mice immunized with HSP70 or HSP70-pulsed DCs survived significantly longer. Although only 60% of the HSP70-immunized mice survived, all mice immunized with HSP70-pulsed DCs survived without MRD. In addition, the cytotoxicities against A20 cells for splenocytes from mice immunized with HSP70-pulsed DCs were significantly higher than those of HSP70-immunized mice, and the cytotoxicities against A20 cells were significantly blocked by anti-CD8 antibody and by major histocompatibility complex class I antibody, but not by anti-CD4 antibody. Moreover, abnormalities were detected in neither the biochemical data nor the histopathologic findings. These findings indicate that the combined use of DCs and leukemia cell-derived HSP70 enhances the antileukemia effect by inducing the specific cytotoxicities of CD8+ cytotoxic T-cells, thereby eradicating MRD effectively and safely, even in an immunocompromised state after syngeneic SCT. This approach may thus be useful for further application of HSP in leukemia patients after autologous SCT.

Induction of leukemia‐specific antibodies by immunotherapy with leukemia‐cell‐derived heat shock protein 70

“…( 17,42,43 ) We have also reported that effective CTL activities are detected in the week after the last immunization of mice with A20‐cell‐derived HSP70. ( 16,17 ) On the other hand, MFI of anti‐A20‐cell antibodies at the third week from the last A20‐HSP70 immunization was the highest from our results of flow cytometry. These results are almost consistent with results from previous studies of immunotherapy with other immunogens.…”

“…Cell‐mediated Th1 immune response is regarded to be a major mechanism of tumor eradication in HSP‐based immunotherapy, ( 5,6 ) and several studies enhancing cell‐mediated immune response have been reported. ( 17,42,43 ) We have also reported that effective CTL activities are detected in the week after the last immunization of mice with A20‐cell‐derived HSP70. ( 16,17 ) On the other hand, MFI of anti‐A20‐cell antibodies at the third week from the last A20‐HSP70 immunization was the highest from our results of flow cytometry.…”

“…( 13–15 ) We have established a mouse model with a minimum amount of leukemia cells after syngeneic bone marrow transplantation, and have reported that the immunization of mice with leukemia‐cell‐derived HSP70 or gp96 induces leukemia‐specific immunities by CD8 positive (+) cytotoxic T‐cells (CTL) and prolongs the survival of the mice. ( 16,17 ) These findings showed the possibility of a clinical application of HSP‐based immunotherapy for patients with leukemia, especially for those with minimal residual leukemia cells after SCT.…”

“…The purification of HSP70 was performed as follows. ( 16,17 ) A pellet of A20 cells or BALB/c mice liver was homogenized in hypotonic buffer (10 mM NaHCO 3 and 0.5 mM phenylmethylsulfonylfluoride: PMSF, pH 7.1) and centrifuged at 100 000 g for 90 min at 4°C. After the supernatant was applied to a PD10‐column (Amersham Pharmacia Biotech) to remove low molecular weight materials, the eluted sample was applied to an adenosine 5′‐diphosphate (ADP)–agarose column.…”

Heat shock protein vaccination and directed IL-2 therapy amplify tumor immunity rapidly following bone marrow transplantation in mice

“…[73][74][75] In contrast to the present studies, 2 to 4 times the amount of gp96 was required, and the first vaccination was administered 2 weeks after HSCT, with subsequent vaccinations after the emergence of thymic-derived T cells. Notably, in our immediate vaccination strategy, although recipient APCs initially contributed to eliciting tumor-reactive CD8 1 T cells (Figure 2A), the response rapidly became singularly dependent on donor B7-expressing APCs ( Figure 2B), which included a critical CD11c 1 CD8a 1 cross-presenting DC population ( Figure 2C) and required perforin-1 ( Figure 2D).…”