Successful Adoptive Immunotherapy Research Articles

Successful adoptive immunotherapy with vaccine-sensitized T cells, despite no effect with vaccination alone in a weakly immunogenic tumor model.

Tumor cell vaccines have been successful at inducing immunity in naïve mice, but only in a few reports has vaccination alone induced regression of established tumors and, generally, only when they are very small. Clinically, vaccinations alone may not be able to cause regression of established human cancers, which tend to be weakly immunogenic. We hypothesized that pharmacologic ex vivo amplification of a vaccination-induced immune response with subsequent adoptive immunotherapy (AIT) to tumor-bearing animals would be more effective in treatment of these animals than vaccination alone. The 4T1 and 4T07 mammary carcinomas are derived from the same parental cell line, but 4T1 is much less immunogenic and more aggressive than 4T07. Vaccination with either 4T1, 4T1-IL-2, or 4T07-IL-2 was not effective as treatment for established 4T1 tumors. However, 4T1 or 4T07-IL-2-vaccine-sensitized draining lymph node (DLN) cells, activated ex vivo with bryostatin 1 and ionomycin and expanded in culture, induced complete tumor regressions when adoptively transferred to 4T1 tumor-bearing animals. This was effective against small tumors as well as more advanced tumors, 10 days after tumor cell inoculation. Furthermore, as would be required for this approach to be used clinically, vaccine-DLN cells obtained from mice with established progressive 4T1 tumors (inoculated 10 days before vaccination) also induced regression of 4T1 tumors in an adoptive host. In none of these experiments was exogenous IL-2 required to induce tumor regression. The response to tumor cell vaccine can be amplified by ex vivo pharmacologic activation of sensitized T cells, which can then cure an established, weakly immunogenic and highly aggressive tumor that was resistant to vaccination alone.

Therapeutic efficacy of adoptive immunotherapy is predicated on in vivo antigen-specific proliferation of donor T cells

Activated T cells with down-regulated L-selectin expression (L-sel −) from tumor-draining lymph nodes represent a potent source of specific immune effectors in adoptive immunotherapy. Using congenic pairs of mice and carboxyfluorescein diacetate succinimidyl ester-labeled L-sel − T cells, the current study analyzed in vivo proliferation of transferred cells. In the lung of MCA205 tumor-bearing mice, 6% or 0.3 × 10 6 of the 5 × 10 6 donor cells were identified 24 h after transfer. Vigorous proliferation of donor cells was evident on day 2, reaching a maximum on day 6. The proliferation was tumor-specific and CD4 T cells divided with greater magnitude than CD8 cells. Successful adoptive immunotherapy also required sublethal whole-body irradiation (WBI) of the recipient. WBI exerted its effects on facilitating specific T cell proliferation at the tumor site. Taken together, our results demonstrate that adoptively transferred T cells undergo extensive proliferation in response to the tumor and this response is associated with therapeutic efficacy.

IL-2 during in vitro priming promotes subsequent engraftment and successful adoptive tumor immunotherapy by persistent memory phenotypic CD8(+) T cells.

Adoptive T cell tumor immunotherapy potentially consists of two protective components by the transferred effector cells, the immediate immune response and the subsequent development of memory T cells. The extent by which adoptively transferred CD8(+) CTL are destined to become memory T cells is ambiguous as most studies focus on the acute effects on tumor shortly following adoptive transfer. In this study we show that a substantial fraction of the input CTL develop into memory cells that reject a s.c. tumor challenge. The use of exogenous IL-2 or a combination of IL-2 and IL-4, but not solely IL-4, during the ex vivo culture for the CTL inoculation was necessary for efficient development of CD8(+) memory T cells. Thus, an important component of adoptive immunotherapy using CTL is the production of CD8(+) Ag-specific memory cells which is primarily favored by IL-2 receptor signaling during ex vivo generation of the effector CTL.

The graft-versus-tumor potential of allogeneic cell therapy: an update on donor leukocyte infusions and nonmyeloablative allogeneic stem cell transplantation.

THE BEST, IF NOT ONLY, CURATIVE THERAPY for many patients with hematologic malignancies is allogeneic stem cell transplantation (SCT). It is now generally accepted that successful allogeneic SCT is dependent not only on the intensive conditioning therapy, but also on the anti-leukemic properties of the donor graft. This very important “graft-versus-leukemia” (GVL) effect is independent of the conditioning regimen and it is mediated, at least in part, by mature donor T cells contained in the stem cell graft. In fact, the rationale for some of the earliest trials of bone marrow transplantation were based on the use of allogeneic bone marrow as “adoptive immunotherapy” to destroy residual leukemia cells, and not just as a convenient source for hematopoietic “rescue” after myeloablative therapy (1). Unfortunately, despite many advances in conditioning regimens and supportive care, regimen-related toxicity, relapse, and graft-versus-host disease (GVHD) remain the major obstacles to successful allogeneic SCT. However, the ability to harness the GVL activity of allogeneic donor cells has provided the foundation for newer, safer approaches of allogeneic cell therapy (ACT) that begin to address problems such as relapse, conditioning regimen toxicity, and GVHD. In the past, the only curative therapy for relapsed leukemia after allogeneic SCT had been second SCT, but only at the expense of extensive morbidity, mortality, and very high relapse rates (2,3). Given conclusive preclinical data for important GVL activity and the indirect evidence for GVL reactions in the clinical setting, it was logical to test the potential for donor leukocyte infusions (DLI) to provide antileukemia activity for patients who relapse after allogeneic SCT. It has now been convincingly demonstrated that donor leukocytes can induce a direct GVL reaction in some patients with relapsed leukemia after allogeneic SCT and restore durable complete remissions without the need for any other conditioning therapy. This represents one of the best examples of successful adoptive immunotherapy and demonstrates that it is now possible to exploit the potent immunological properties of the human immune system for clinical benefit. The use of DLI for relapsed leukemia has led to trials using allogeneic adoptive immunotherapy as primary cancer therapy, either as primary DLI or with the use of nonmyeloablative conditioning and allogeneic SCT. Although many issues remain unsettled, the potential to harness the more general “graftversus-tumor” (GVT) activity of allogeneic donor cells may provide a new paradigm for allogeneic cell transplantation and the immunotherapy of cancer.

Cancer-induced Defective Cytotoxic T Lymphocyte Effector Function: Another Mechanism How Antigenic Tumors Escape Immune-mediated Killing

The notion that a deficit in immune cell functions permits tumor growth has received experimental support with the discovery of several different biochemical defects in T lymphocytes that infiltrate cancers. Decreased levels of enzymes involved with T-cell signal transduction have been reported by several laboratories, suggesting that tumors or host cells recruited to the tumor site actively down-regulate antitumor T-cell immune response. This permits tumor escape from immune-mediated killing. The possibility that defects in T-cell signal transduction can be reversed, which would potentially permit successful vaccination or adoptive immunotherapy, motivates renewed interest in the field. Summarizing the literature concerning tumor-induced T-cell dysfunction, we focus on the end stage of immune response to human cancer, that of defective cytotoxic T lymphocyte killing function. Based on the data from several laboratories, we hypothesize a biochemical mechanism that accounts for the unusual phenotype of antitumor T-cell accumulation in tumors, but with defective killing function.

Tumor Infiltration by Adoptively Transferred T Cells Is Independent of Immunologic Specificity but Requires Down-Regulation of L-Selectin Expression

Adoptive immunotherapy with anti-CD3/IL-2 activated tumor-draining lymph node (LN) T cells is capable of eradicating tumor established at various histological sites. Tumor-specific effector lymphocytes have recently been identified to be LN T cells with down-regulated L-selectin (L-selectin-). Using fluorochrome labeling, the present study determined the early trafficking pattern of systemically transferred cells. In mice with 10-day established pulmonary 3-methylcholanthrene (MCA) 205 metastases, accumulation of cells in tumors was evident as early as 2 h after i.v. cell transfer, and, by 24 h, >50-fold higher numbers of cells were seen in metastases than in normal tissues. Similarly, transferred cells selectively infiltrated s.c. tumors, albeit at a lower rate. Analysis of the transferred cells isolated from recipient mice revealed that tumor-infiltrating cells were mostly L-selectin- (>95%). By contrast, only 24% and 58% L-selectin- cells were found in the LN and spleen, respectively. The ability of L-selectin- cells to accumulate at tumor sites was confirmed by the transfer of purified cell populations. Despite this selective tumor infiltration, the trafficking pattern did not reflect antigenetic specificity, and tumor regression occurred only after the transfer of tumor-specific effector cells. These results, thus, suggest that there are two distinct mechanisms operative in successful adoptive immunotherapy. Early infiltration of tumors by transferred cells is dictated by the physiological properties of cells and is independent on their immunologic specificity. Tumor regression, however, requires immunologically specific interactions at the site of tumor.

Successful Adoptive Immunotherapy of MurinePoorly ImmunogenicTumor with Specific Effector Cells Generated from Gene-Modified Tumor-Primed Lymph Node Cells

AbstractWe previously reported that cytokine gene transfer into weakly immunogenic tumor cells could enhance the generation of precursor cells of tumor-reactive T cells and subsequently augment antitumor efficacy of adoptive immunotherapy. We investigated whether such potent antitumor effector T cells could be generated from mice bearing poorly immunogenic tumors. In contrast to similarly modified weakly immunogenic tumors, MCA102 cells, which are chemically induced poorly immunogenic fibrosarcoma cells transfected with cDNA for IL-2, IL-4, IL-6, IFN-γ, failed to augment the host immune reaction. Because priming of antitumor effector T cells in vivo requires two important signals provided by tumor-associated Ags and costimulatory molecules, these tumor cells were cotransfected with a B7-1 cDNA. Transfection of both IFN-γ and B7-1 (MCA102/B7-1/IFN-γ) resulted in regression of s.c. tumors, while tumor transfected with other combinations of cytokine and B7-1 showed progressive growth. Cotransfection of IFN-γ and B7-1 into other poorly immunogenic tumor B16 and LLC cells also resulted in the regression of s.c. tumors. Cells derived from lymph nodes draining MCA102/B7-1/IFN-γ tumors showed potent antitumor efficacy, eradicating established pulmonary metastases, but this effect was not seen with parental tumors. This mechanism of enhanced antitumor efficacy was further investigated, and T cells with down-regulated L-selectin expression, which constituted all the in vivo antitumor reactivity, were significantly increased in lymph nodes draining MCA102/B7-1/IFN-γ tumors. These T cells developed into potent antitumor effector cells after in vitro activation with anti-CD3/IL-2. The strategy presented here may provide a basis for developing potent immunotherapy for human cancers.

The graft-versus-leukemia effects of allogeneic cell therapy.

Until recently, the only cure for relapse after allogeneic bone marrow transplantation (BMT) has been a second BMT. Recently, infusions of leukocytes collected from the original transplant donor have been used to induce a direct graft-versus-leukemia (GVL) reaction in patients with relapsed disease. Adoptive immunotherapy with donor leukocyte infusions (DLI) results in complete remission for 60-80% of patients with relapsed chronic-phase CML; therapy is also effective for relapse of diseases other than CML, although response rates are lower. Adoptive immunotherapy induces remissions for the majority of patients with post-transplantation Epstein-Barr virus-related lymphomas and other viral-associated illnesses. The extraordinary success of DLI demonstrates that it is now possible to harness the GVL potential of the human immune system for clinical benefit. The necessary effector cells and target antigens required for GVL reactivity are poorly defined but are the subject of intensive investigation. Future trials will investigate strategies that retain and enhance the GVL effects while limiting toxicity from this therapy, and they may define methods of successful allogeneic adoptive immunotherapy outside the setting of allogeneic BMT.

Successful adoptive immunotherapy for relapse of AML 9 years after T‐cell‐depleted BMT

Relapse is one of the main problems which can occur following allogeneic transplantation for haematological malignancies. In this situation the enhancement of the graft-versus-leukaemia effect by transfusion of donor buffy coats with or without cytokines may lead to complete remission especially in myeloid leukaemias. FISH (fluorescence in situ hybridization) is a sensitive method to monitor chimaerism in gender-different transplantation. We report a case of successful buffy coat transfer therapy > 9 years after bone marrow transplantation. This is the longest interval reported, to our knowledge, between transplantation to relapse, which was treated by adoptive immunotherapy. Complete donor chimaerism was confirmed by FISH.

Successful Adoptive Cellular Immunotherapy Is Dependent on Induction of a Host Immune Response Triggered by Cytokine (IFN-γ and Granulocyte/Macrophage Colony-Stimulating Factor) Producing Donor Tumor-Infiltrating Lymphocytes

Abstract Adoptive immunotherapy with tumor-infiltrating lymphocytes (TIL) and systemic low dose rIL-2 effectively eradicates pulmonary metastases of the murine MCA-105 sarcoma. We described earlier that host CD8+ T cells are critical for tumor eradication and that successful treatment is associated with production of high levels of IFN-γ and granulocyte/macrophage (GM)-CSF by donor TIL in vitro. Here, we propose the mechanism through which adoptively transferred Thy-1.1+ TIL induce a host antitumor response in congenic Thy-1.2+ tumor-bearing mice. Donor Thy-1.1+ TIL were detected at the tumor site 12 h after transfer. These Thy-1.1+ cells produced IFN-γ and GM-CSF in situ. The percentage of Thy-1.1+ TIL at the tumor site increased up to 16.4 ± 4.9% 24 h after transfer but decreased to undetectable levels thereafter. In contrast, the percentages of host cells producing IFN-γ and GM-CSF continued to increase at the tumor site. These increases were significantly higher in TIL + rIL-2-treated mice compared with untreated mice and rIL-2-treated mice 48 h after TIL transfer. The appearance of IFN-γ+ and GM-CSF+ cells was followed by a large influx of host CD4+, CD8+, and Thy-1.2+ TIL and eventually by tumor eradication. This response was tumor specific since TIL obtained from MCA-205 did not induce high levels of IFN-γ and GM-CSF and did not induce tumor eradication of MCA-105 tumor. Coinjection of Thy-1.1+ TIL and anti-IFN-γ or anti-GM-CSF mAb significantly inhibited antitumor efficacy of the TIL + rIL-2 treatment. We conclude that successful adoptive immunotherapy in this model is mediated through cytokine production by adoptively transferred TIL that induce a host T cell-dependent antitumor response.

Activated T cells and cytokine-induced CD3+CD56+ killer cells.

Over the past two decades, attempts have been made to develop immunotherapy for patients with cancer. A significant obstacle to the development of successful adoptive immunotherapy has been the availability of appropriate cytotoxic cells. Immunologic effector cells such as lymphokine-activated killer (LAK) cells, activated T cells such as tumor-infiltrating lymphocytes (TILs), and cytokine-induced killer (CIK) cells may be suitable to remove residual tumor cells.

Adoptive immunotherapy involving recombinant human M-CSF and R24 anti-melanoma antibody induces human T-cell infiltration into human melanoma xenografts.

Directed motion toward and infiltration of tumor masses by effector cells is essential for successful adoptive immunotherapy. A human/SCID mouse chimeric system was used to examine whether an antitumor antibody and recombinant human monocyte colony-stimulating factor (rhM-CSF) could promote human T-cell infiltration of a human tumor in vivo. Fourteen days after subcutaneous injection of the human melanoma cell line M-14 into SCID recipients, several adoptive immunotherapy regimens were initiated using activated human T cells, an anti-melanoma monoclonal antibody (MoAb) (R24), and rhM-CSF. Effects on tumor growth and human T-cell infiltration into the tumor were assessed. Compared with other treatment groups, only mice treated with the combination of activated human T cells, anti-tumor MoAb, and rhM-CSF demonstrated a significant cellular infiltrate in the melanoma. Immunohistology demonstrated human T cells present in the tumor up to 7 days after injection. Groups treated with rhRANTES or rmGM-CSF in place of rhM-CSF exhibited markedly less human T-cell infiltration. Additionally, only mice treated with human T cells, R24, and rhM-CSF demonstrated a significant antitumor response in vivo. This model suggests that activated human T cells can be specifically targeted to in vivo tumor sites by combined treatment with an antitumor antibody and rhM-CSF.

Efficient tumor eradication by adoptively transferred cytotoxic T-cell clones in allogeneic hosts

Tumor-specific cytotoxic T cells (CTLs) can play an important role against cancer as illustrated by the observation that adoptive transfer of tumor-specific CTLs can mediate potent anti-tumor effects. Although such CTLs can be detected at the tumor site, relatively little is known about the mechanisms by which they enter the tumor. In this study, the role of major histocompatibility complex (MHC) class 1 molecules on vascular endothelium in the tumor in entry of, and tumor eradication by, tumor-specific CTL was investigated. Two H-2Db-restricted CTL clones recognizing peptide VNIRNCCYI on human adenovirus type 5 early region 1-(Ad5E1)-induced tumors were used to test whether CTLs were able to cross the vascular endothelium lacking the restricting MHC molecule. One CTL clone recognizes peptide VNIRNCCYI in the context of both H-2Db and H-2Dbm14 molecules. The other CTL clone recognizes this peptide only in the context of H-2Db. Adoptive transfer of these CTLs leads to eradication of Ad5E 1-induced, H-2Db-expressing tumors in B6(H-2Db+) and Bm14(H-2Db-) nude mice. Our data show that presentation of tumor-derived peptides by MHC molecules on endothelial cells of blood vessels in a tumor do not play a major role in eradication of tumors by adoptively transferred CTL in combination with interleukin-2. Moreover, our data show that successful adoptive CTL immunotherapy is possible across allogeneic barriers, without inducing severe side effects, provided the tumor expresses the MHC class 1-peptide complex recognized by the CTLs.

Principles for adoptive T cell therapy of human viral diseases.

The development of successful adoptive immunotherapy for human virus infections is predicated on an understanding of the effector cells and mechanisms essential for providing the host with a protective response to acute infection and the requirements for long-term in vivo survival of transferred cells that will be necessary to provide memory responses to persistent and latent viral infections. In this review, we discuss the results of recent studies examining the effector mechanisms mediated by virus-specific alpha beta + T cells and the strategies viruses have evolved to evade recognition by such T cells and/or to interfere with the expression of T cell effector functions. The evasion strategies employed by individual viruses can render T cell subsets or T cells of particular specificities less effective in eliminating virally infected cells, and consequently they are less desirable choices for use in adoptive therapy. Insights derived from described studies of the pathogenesis and immunobiology of virus infections have resulted in the development of clinical adoptive immunotherapy studies for infections with CMV, EBV, and HIV. Although the results from such studies are preliminary, the principle that virus-specific T cells can be successfully transferred and can mediate therapeutic efficacy in humans has already been affirmed. The use of recently developed methods, such as retroviral-mediated gene transfer, to genetically modify antigen-specific T cell clones provides a novel approach to overcome limitations and improve on the safety and efficacy observed in these initial studies, suggesting that more widespread use of adoptive transfer of specific T cells as a therapeutic regimen should be feasible in the near future.

Principles for Adoptive T Cell Therapy of Human Viral Diseases

The development of successful adoptive immunotherapy for human virus infections is predicated on an understanding of the effector cells and mechanisms essential for providing the host with a protective response to acute infection and the requirements for long-term in vivo survival of transferred cells that will be necessary to provide memory responses to persistent and latent viral infections. In this review, we discuss the results of recent studies examining the effector mechanisms mediated by virus-specific αβ+ T cells and the strategies viruses have evolved to evade recognition by such T cells and/or to interfere with the expression of T cell effector functions. The evasion strategies employed by individual viruses can render T cell subsets or T cells of particular specificities less effective in eliminating virally infected cells, and consequently they are less desirable choices for use in adoptive therapy. Insights derived from described studies of the pathogenesis and immunobiology of virus infections have resulted in the development of clinical adoptive immunotherapy studies for infections with CMV, EBV, and HIV. Although the results from such studies are preliminary, the principle that virus-specific T cells can be successfully transferred and can mediate therapeutic efficacy in humans has already been affirmed. The use of recently developed methods, such as retroviral-mediated gene transfer, to genetically modify antigen-specific T cell clones provides a novel approach to overcome limitations and improve on the safety and efficacy observed in these initial studies, suggesting that more widespread use of adoptive transfer of specific T cells as a therapeutic regimen should be feasible in the near future.

Activation of T lymphocytes for the adoptive immunotherapy of cancer

Adoptive immunotherapy of malignancy involves the passive transfer of antitumor-reactive cells into a host in order to mediate tumor regression. Based on animal models, the transfer of immune lymphoid cells can eradicate widely disseminated tumors and establish long-term systemic immunity. Critical for successful adoptive immunotherapy is the ability to isolate large numbers of immune cells. For clinical therapy, it will require the development on in vitro methods to promote the sensitization and propagation of tumor-reactive cells. However, this is a formidable task since human cancers are postulated to be poorly immunogenic because of their spontaneous origins. Human lymphoid cells for ex vivo activation and subsequent adoptive transfer have been derived from different sources, including peripheral blood, tumor, and lymph nodes. Peripheral blood lymphocytes can be incubated with interleukin 2 to generate lymphokine-activated killer (LAK) cells, which nonspecifically lyse autologous and allogeneic tumor cells in vitro. LAK cell therapy represented the earliest attempt to treat advanced human cancers, with encouraging results documented in patients with renal cell cancer and melanoma. From that experience, the use of more immunologically specific cellular agents with potentially greater therapeutic efficacy has been investigated. One approach uses tumor-infiltrating lymphocytes, which have been characterized experimentally to be more specific in tumor reactivity compared with LAK cells. Other techniques have involved the use of lymphoid cells derived from lymph nodes draining tumors or primed by tumor vaccines. In vitro activation of these cells with tumor antigen or anti-CD3 monoclonal antibody results in the generation of T cells that mediate the rejection of poorly immunogenic tumors in animal studies. These alternate methods are currently being evaluated in clinical studies. Experimentally, cellular therapy is a potent method to eradicate progressive tumors. Initial clinical studies have demonstrated that this form of therapy is technically feasible and can result in meaningful antitumor responses. Advances in this area will require improved methods to sensitize, isolate, and expand tumor-reactive T cells for adoptive transfer.

Successful Adoptive Immunotherapy with Lymphokine-activated Killer Cells in the Treatment of Medulloblastoma Disseminated via Cerebrospinal Fluid

Successful Adoptive Immunotherapy with Lymphokine-activated Killer Cells in the Treatment of Medulloblastoma Disseminated via Cerebrospinal Fluid

Successful Adoptive Immunotherapy with Lymphokine-activated Killer Cells in the Treatment of Medulloblastoma Disseminated via Cerebrospinal Fluid

We report the case of a girl who developed cerebellar medulloblastoma at the age of 12 years and in whom, 4 years after surgical removal and radiotherapy, neoplastic dissemination via the cerebrospinal fluid took place. After only partially effective systemic and intrathecal chemotherapy, an intrathecal administration of lymphokine-activated killer cells and recombinant interleukin-2 allowed complete clinical recovery persisting after a follow-up of 30 months.

Kinetics of interleukin-2 induced changes in rigidity of human natural killer cells.

The success of adoptive immunotherapy is dependent in part on the successful delivery of effector cells to the tumor and the expression of cellular activities, such as adhesion, extravasation, and cytotoxic activity of the effector cells in the tumor. The structural rigidity of the effector cell is an important determinant of these functions. The present study was designed to quantify the changes in cellular rigidity and cytotoxic activity of human natural killer (NK) cells in the presence or absence of interleukin-2 (IL-2). Micropipet aspiration was used to measure the resistance of NK cells to an imposed external deformation. Homogeneous suspensions of NK cells were activated with 1000 U/mL of recombinant IL-2 in vitro and tested for cellular rigidity from 0 to 96 h post stimulation. The IL-2 activated cells increased their rigidity within 24 h and maintained it at this level for 96 h. Prolonged incubation of cells in IL-2 (14 d) resulted in a consistently high rigidity, which was further increased on starvation of the cells from IL-2. The increased rigidity of these cells was maintained throughout 96 h of IL-2 deprivation, although significant relaxation of rigidity was observed between 48 and 96 h. The relaxation of rigidity was associated with an increase in the number of nonviable cells. Reintroduction of IL-2 for 24 h to a culture of NK cells depleted of IL-2 for 48 h did not restore the cells to the pre-depletion level of rigidity. Cytotoxic activity of the activated NK cells following removal of IL-2 decreased to about 60% of the control activity within 24 h and continued through 72 h post-deprivation. These findings suggest that the initial activation of human NK cells by IL-2 will produce a relatively rapid increase in rigidity that may cause entrapment of these cells in small capillaries in vivo and that removal of IL-2 will produce an additional increase in rigidity, which is associated with decreased functional activity.

Successful adoptive immunotherapy with OK432-inducible activated natural killer cells in tumor-bearing mice

We had demonstrated that the NK cell mediated cytotoxicity of murine spleen cells could be augmented by in vivo priming and subsequent in vitro challenge with a streptococcal preparation OK432, and the cell surface phenotype of induced killer cells was Thy-1+, asialo GM1+, suggesting that the activated cells were of NK lineage (OK-NK cell). We had also clarified that IL-2 played a major role in inducing the OK-NK cells via the production of IFN-gamma. In this study, we examined the effect of adoptive transfer of OK-NK cells on syngeneic tumors in mice. Mice were implanted with SP2 myeloma cells intraperitoneally (i.p.), or C26 colon adenocarcinoma cells subcutaneously to make the models of peritonitis carcinomatosa or solid tumor, and the OK-NK cells were transferred i.p. or intratumorally, adoptively. By the adoptive transfer of OK-NK cells, 92% of mice bearing SP2-tumor had be cured. The tumor growth of C26-solid tumor was inhibited, and the survival rate of mice bearing C26-tumor was significantly increased. The intratumoral remnants of 125I-labelled OK-NK cells were 61, 27 and 8% at 4, 12 and 36h after intratumoral transfer, respectively. By multiple transfer of OK-NK cells, the antitumor effect was more effectively augmented than that of a single transfer. Results in this study suggested that OK-NK cells could be useful for the therapy of cancer patients.