Impact of modern systemic therapies and clinical markers on treatment outcome for metastatic melanoma in a real-world setting.

BACKGROUND: The survival in metastatic melanoma has dramatically improved after the introduction of immune checkpoint- (ICIs) and MAPKinase inhibitors (MAPKis). OBJECTIVE: Our aim was to describe therapy response and survival in a real-world population as well as to assess the associations between clinical variables and therapy outcome for patients with metastatic melanoma receiving first-line ICIs or MAPKis. METHODS: A total of 252 patients with metastatic (stage IV) melanoma were prospectively followed between 1 January 2010 and 3 December 2017 with follow-up until 31 March 2019, at the Karolinska University Hospital, Sweden. Hazard ratios (HRs) for progression-free survival (PFS) and overall survival (OS) were analysed with Cox regression, and logistic regression was used to estimate odds ratios (ORs) for therapy response. RESULTS: Patients receiving ICIs (n = 138) experienced longer PFS compared to patients that received MAPKis (n = 114; median PFS for ICIs was 6.8 months, and median PFS for MAPKis was 5.3 months). In the multivariable analyses of clinical markers, increasing M-stage (OR 0.65; 95% CI 0.45-0.94; P = 0.022) and male sex (OR 0.41; 95% CI 0.19-0.90; P = 0.027) were significantly associated with lower response to ICIs. Lower baseline albumin levels (OR 0.90; 95% CI 0.83-0.98; P = 0.019) and male sex (OR 0.33; 95% CI 0.12-0.93; P = 0.036) were related with lower response to MAPKis. For ICIs, increasing M-stage (HR 1.34; 95% CI 1.07-1.68; P = 0.010), increasing LDH (HR 1.73; 95% CI 1.19-2.50; P = 0.004) and decreasing albumin (HR 1.06; 95% CI 1.01-1.10; P = 0.011) were significantly associated lower PFS in the adjusted model. The corresponding markers for MAPKis were increasing LDH (HR 1.44; 95% CI 1.08-1.92; P = 0.013) and decreasing albumin (HR 1.05; 95% CI 1.02-1.09; P = 0.005) for PFS. CONCLUSION: ICIs and MAPKis were effective in this real-world population, and we could confirm the importance of previously reported clinical prognostic markers. Albumin values may be associated with therapy outcome but need further validation.

Immunoscore and Immunoprofiling in cancer: an update from the melanoma and immunotherapy bridge 2015.

The fifth "Melanoma Bridge Meeting" took place in Naples, December 1-5th, 2015. The main topics discussed at this meeting were: Molecular and Immuno advances, Immunotherapies and Combination Therapies, Tumor Microenvironment and Biomarkers and Immunoscore. The natural history of cancer involves interactions between the tumor and the immune system of the host. The immune infiltration at the tumor site may be indicative of host response. Significant correlations were shown between the levels of immune cell infiltration in tumors and patient's clinical outcome. Moreover, incredible progress comes from the discovery of mutation-encoded tumor neoantigens. In fact, as tumors grow, they acquire mutations that are able to influence the response of patients to immune checkpoint inhibitors. It has been demonstrated that sensitivity to PD-1 and CTLA-4 blockade in patients with advanced NSCLC and melanoma was enhanced in tumors enriched for clonal neoantigens. The road ahead is still very long, but the knowledge of the mechanisms of immune escape, the study of tumor neo-antigens as well as of tumor microenvironment and the development of new immunotherapy strategies, will make cancer a more and more treatable disease.

Marizomib for patients with newly diagnosed glioblastoma: a randomized phase 3 trial.

BACKGROUND: Standard treatment for patients with newly diagnosed glioblastoma includes surgery, radiotherapy (RT) and temozolomide (TMZ) chemotherapy (TMZ/RT→TMZ). The proteasome has long been considered a promising therapeutic target because of its role as a central biological hub in tumor cells. Marizomib is a novel pan-proteasome inhibitor that crosses the blood brain barrier. METHODS: EORTC 1709/CCTG CE.8 was a multicenter, randomized, controlled, open label phase 3 superiority trial. Key eligibility criteria included newly diagnosed glioblastoma, age > 18 years and Karnofsky performance status > 70. Patients were randomized in a 1:1 ratio. The primary objective was to compare overall survival (OS) in patients receiving marizomib in addition to TMZ/RT→TMZ with patients receiving only standard treatment in the whole population, and in the subgroup of patients with MGMT promoter-unmethylated tumors. RESULTS: The trial was opened at 82 institutions in Europe, Canada and the US. A total of 749 patients (99.9% of planned 750) were randomized. OS was not different between the standard and the marizomib arm (median 17 vs 16.5 months; HR=1.04; p=0.64). PFS was not statistically different either (median 6.0 vs. 6.3 months; HR=0.97; p=0.67). In patients with MGMT promoter-unmethylated tumors, OS was also not different between standard therapy and marizomib (median 14.5 vs 15.1 months, HR=1.13; p=0.27). More CTCAE grade 3/4 treatment-emergent adverse events were observed in the marizomib arm than in the standard arm. CONCLUSIONS: Adding marizomib to standard temozolomide-based radiochemotherapy resulted in more toxicity, but did not improve OS or PFS in patients with newly diagnosed glioblastoma.

Myeloid-derived suppressor cells impair the quality of dendritic cell vaccines.

Myeloid-derived suppressor cells (MDSC) are important regulators of the immune system and key players in tumor-induced suppression of T-cell responses. CD14+HLA-DR-/low MDSC have been detected in a great number of malignancies, including melanoma. MDSC are known to be impaired in their ability to differentiate along the myeloid lineage, e.g., into dendritic cells (DC). This is a concern for utilization of monocyte-derived DC for vaccination of patients with melanoma or other cancers exhibiting accumulation of CD14+ MDSC. When producing DC according to standard operating procedures of two currently ongoing clinical trials, we found that MDSC co-purified with monocytes isolated by elutriation. MDSC frequencies did not affect yield or viability of the produced DC, but induced a dose-dependent decrease in DC maturation, ability to take up antigen, migrate and induce T-cell IFNγ production. Changes in DC characteristics were most notable when 'pathological' frequencies of >50% CD14+HLA-DR- cells were present in the starting culture. The impaired DC quality could not be explained by altered cytokine production or increased oxidative stress in the cultures. Tracking of HLA-DR- cells throughout the culture period revealed that the observed changes were partially due to the impaired maturation and functionality of the originally HLA-DR- population, but also to their negative effects on HLA-DR+ cells. In conclusion, MDSC could be induced to differentiate into DC but, due to the impairment of overall DC vaccine quality when >50% HLA-DR- cells were present in the starting culture, their removal could be advisable.

Interleukin 10 pretreatment protects target cells from tumor- and allo-specific cytotoxic T cells and downregulates HLA class I expression.

Interleukin 10 (IL-10) is a cytokine with a variety of reported effects including inhibition of monocyte major histocompatibility complex (MHC) class II-dependent antigen presentation, type 1 helper T cell cytokine production, and inhibition of T cell proliferation. Herein we report the effect of IL-10 pretreatment on antigen presentation to tumor- and allo-specific CD8+ cytotoxic T lymphocytes (CTL). Prior incubation of human melanoma cells with recombinant IL-10 (rIL-10) for 48-72 h resulted in a dose-dependent, up to 100% inhibition, of autologous CTL-mediated, HLA-A2.1-restricted, tumor-specific lysis. Allo-specific CTL cytotoxicity against Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL) was also inhibited, demonstrating a protective effect also on lymphoid cells. In contrast, IL-10 pretreatment of allogeneic LCL or K562 targets had either no effect or slightly enhanced cytotoxic activity mediated by freshly isolated or IL-2-activated natural killer cells. Flow cytometric analysis with monoclonal antibodies against HLA-A2, or nonpolymorphic determinants of MHC class I proteins, revealed a 20-50% reduction in cell-surface expression, whereas intercellular adhesion molecules 1, and 2, and lymphocyte function-associated antigen 3 levels were not affected. In addition, relative to untreated target cells, IL-10 pretreated tumor cells were unaltered in their capacity to affect CTL-mediated lysis by cold target inhibition, demonstrating that the effect of IL-10 is unrelated to the initial binding of CTL to their targets. These results are compatible with an effect of IL-10 on the MHC class I antigen presentation pathway, and suggest a novel mechanism of immune tolerance, based on escape from CTL-mediated tumor and allo-transplant rejection.

Human lymphoma-lymphoma hybrids and lymphoma-leukemia hybrids. I. Isolation, characterization, cell surface markers, and B-cell markers.

Four new somatic cell hybrids were obtained by fusion of various Burkitt's lymphoma (BL)-derived cell lines that had different selective markers: Raji-P3HR-1, Daudi-Raji, and a P3HR-1-P3HR-1 "autohybrid" derived from two P3HR-1 sublines. In addition, a hybrid was obtained between the Daudi (BL) line and the human leukemia cell line K562. The hybrids were extensively characterized by means of chromosome, isozyme, and HLA surface markers. The phenotypic differences between the parent cell lines allowed some conclusions with respect to the expression of latent Epstein-Barr virus (EBV) genomes, C3 and EBV receptors, and of immunoglobulin and beta 2-microglobulin-HLA expression as well as the influence of the leukemia cell (K562) genome on B-cell properties in the Daudi-K562 hybrid. B-cell and differentiated markers of these hybrids were characterized. High-level expression dominated for the marker C3 and EBV receptors, which showed a good correlation coefficient of 0.84, as was true for Fc receptors and surface immunoglobulin. The Daudi-K562 hybrid showed loss of all B-cell markers but retention of the leukemia cell markers (e.g., hemoglobin synthesis).

Hybridization of a myeloid leukemia-derived human cell line (K562) with a human Burkitt's lymphoma line (P3HR-1).

The myeloid leukemia-derived Epstein-Barr virus (EBV)-negative human lymphoid cell line K562 was successfully hybridized with the EBV-carrying Burkitt's lymphoma line P3HR-1. Authenticity of the hybrid PUTKO-1 was established by chromosome and isoenzyme studies. A virtually complete hybrid PUTKO-1 carried the EBV genome derived from the lymphoma parent. It averaged 26 EBV DNA copies per cell and was 100% positive for Epstein-Barr virus-associated nuclear antigen (EBNA). In most respects, the hybrid resembled the K562 parent: It had a high Fc receptor concentration, high sensitivity to natural killer cells, absence of EBV C3 receptors, and deficiency of membrane-associated beta 2-microglobulin (beta 2M) and HLA, in parallel with intracellular synthesis and secretion of beta 2M to the medium. Unlike the P3HR-1 parent, the hybrid was completely nonpermissive for antigens of the EBV cycle, early antigen, and viral capsid antigen. None of the 3 inducing agents, 5-lodo-2'-deoxyuridine, 12-O-tetradecanoyl-phorbol 13-acetate, or sodium butyrate, caused any viral antigen synthesis in PUTKO-1 in contrast to the good inducibility of the parental P3HR-1 subline. Thus the myeloid parent restricted expression of EBV antigens except EBNA. This exception further supports the concept that EBNA is an autonomous function of the viral genome, independent of host cell control that regulates expression of antigens related to the viral cycle. On the contrary, extinction of viral antigens in this hybrid between 2 cell lineages supports our previous concept that the ability to produce viral antigens is similar to a differentiated B-cell property.

T-cell response to B-cells and Epstein-Barr virus antigens in infectious mononucleosis.

After Epstein-Barr virus (EBV) infection in vivo, B-cells with latent virus infection persist indefinitely through life. These cells grow in vitro on explanation and can be established as immortal B-cell lines. To reconcile the unlimited growth potential in vitro with the maintenance of a low proportion of B-cells infected by EBV in vivo, a strict in vivo control mechanism has to be postulated. Certain aspects of this control are apparent when the primary infection is followed by infectious mononucleosis. This is characterized by lymphocytosis and the presence of activated T-cells. The T-cell proliferation is probably the manifestation of the immune response against EBV antigens. However, the reaction of T-cells upon encounter of B-blasts is also likely to contribute to the events. At present, it is difficult to detect an EBV-specific component in the action of the T-cells in the acute phase of mononucleosis exerted on B-cells. However, for the clinical course of the disease the activation of T-cells is important. The activated T-cells may control and also eliminate the B-cells infected by EBV. In addition to the immunity which develops during the disease, th immunoregulatory mechanism is likely to have a role in the inhibition of B-cell proliferation.

Synthetic peptides derived from the melanocyte-stimulating hormone receptor MC1R can stimulate HLA-A2-restricted cytotoxic T lymphocytes that recognize naturally processed peptides on human melanoma cells.

Human melanoma-specific HLA-A2 restricted CTLs have recently been shown to recognize antigens expressed by melanoma lines and normal melanocytes, including Melan-A/Mart-1, gp100, gp75, and tyrosinase. Herein, we define HLA-A2-restricted CTL epitopes from a recently cloned melanocortin 1 receptor (MC1R), which belongs to a new subfamily of the G-protein-coupled receptors expressed on melanomas and melanocytes. Thirty-one MC1R-derived peptides were selected on the basis of HLA-A2-specific motifs and tested for their HLA-A2 binding capacity. Of a group of 12 high or intermediate HLA-A2 binding peptides, three nonamers, MC1R244 (TILLGIFFL), MC1R283 (FLALIICNA), and MC1R291 (AIIDPLIYA), were found to induce peptide-specific CTLs from peripheral blood mononuclear cells of healthy HLA-A2+ donors after repeated in vitro stimulation with peptide-pulsed antigen-presenting cells. The CTLs raised against these three HLA-A2+-restricted peptides could recognize naturally processed peptides from HLA-A2+ melanomas and from Cos7 cells cotransfected with MC1R and HLA-A2. CTLs induced by the MC1R291 peptide (but not induced or induced only to a very low extent by the other two MCR1 peptide epitopes) showed cross-reactions with two other members of the melanocortin receptor family, which are more broadly expressed on other tissues. Taken together, our findings have implications in relation both to autoimmunity and immunotherapy of malignant melanomas.

Immunological characterization of Hodgkin's and non-Hodgkin's lymphoma patients with high antibody titers against Epstein-Barr virus-associated antigens.

We have studied nine Hodgkin's lymphoma (HD) and ten non-Hodgkin's lymphoma (NHL) patients with extraordinarily high anti-viral capsid antigen (VCA) titers (greater than 5120). Controls were 13 HD and 23 NHL patients with anti-VCA titers between 40 and 2560. High anti-VCA titers were present in NHL patients at the time of diagnosis or within 16 months, whereas the rise of anti-VCA titers in HD patients appeared to be a late event during the clinical course of the disease (mean time from diagnosis, 68 months). In particular, we have asked whether the exceptionally high anti-Epstein-Barr virus (EBV) titers in some HD and NHL patients can be correlated to some of the EBV-specific and -nonspecific parameters of cell-mediated immunity. The battery of non-EBV-specific immunological tests included the assessment of natural killer cell activity and the analysis of T-lymphocyte subclasses according to surface markers, together with spontaneous and mitogen-induced DNA synthesis and their helper or suppressor activity on PWM-generated immunoglobulin synthesis. Outgrowth inhibition (Ol) and leukocyte migration inhibition were used to assess EBV-specific cell-mediated immunity. The majority of the high-titer HD and NHL patients showed a drastically reduced OKT4:OKT8 ratio in their peripheral lymphocyte population. Low-titer HD and NHL patients showed no such reduction. There was no strict correlation between the number of OKT8-positive cells and suppressor activity in the functional PWM-induced immunoglobulin production test. Part of the high-titer HD patients showed defective cellular responses in the outgrowth inhibition test, directed against the proliferation of EBV-transformed (EBV-determined nuclear antigen-positive) cells. Some of them showed also a deficient leukocyte migration inhibition response to EBV-determined nuclear antigen but, interestingly, not to early antigen-VCA. In the NHL group, only one of the high-titer patients showed a similar defect. None of the low-titer HD and NHL patients showed such defects.

Cell-mediated immune reactions in three patients with malignant lymphoproliferative diseases in remission and abnormally high Epstein-Barr virus antibody titers.

Two patients with Hodgkin's disease in remission and one chronic lymphatic leukemia patient with extraordinarily high anti-Epstein-Barr virus (EBV) (viral capsid antigen) antibody titers (greater than 10,000) were selected to study a spectrum of cell-mediated immune responses, including natural killer, interferon-boosted killer, antibody-dependent lymphocytotoxicity, and T-cell-mediated reactions. The purpose was to compare these reactions in patients with immunosuppression and a high EBV load who can hold their EBV-carrying cells under control with the corresponding reactions in patients with EBV-carrying lymphoproliferative disease. In contrast to the latter group, the three patients of the present study showed a less profound and less general suppression of the immune responses. Multiple effector mechanisms probably safeguard against the proliferation of EBV-transformed B-cells. Clinically manifest EBV-carrying lymphoproliferative disease occurs only in very severe immunodeficiencies effecting multiple effectors.

Cellular immune defects to Epstein-Barr virus-determined antigens in young males.

Three males with the X-linked lymphoproliferative syndrome (XLP) with hypo- or agammaglobulinemia following Epstein-Barr virus (EBV) infection and two males with the chronic mononucleosis syndrome were investigated for immune responses to EBV-determined antigens. Males with XLP showed profound cellular immune defects. Markedly diminished responses of natural killer cell and interferon-activated killer cell activities and impaired leukocyte migration inhibition responses to phytohemagglutinin were determined in patients with XLP. The two patients with chronic mononucleosis showed less severe defects. All patients showed partial or complete impairment of their EBV-specific immune responses as measured by leukocyte migration inhibition. EBV-specific antibodies were markedly diminished against EBV-associated nuclear antigen, early antigen, and viral capsid antigen in males with XLP. In contrast, patients with chronic mononucleosis had elevated antibodies to most EBV-specific antigens. Individuals with life-threatening EBV-induced lymphoproliferative disorders may exhibit multiple defective immune mechanisms against the virus.

Effects of human plasma proteins on maturation of monocyte-derived dendritic cells.

Dendritic cells (DC) are a promising tool for vaccine therapy due to their unique properties as antigen presenting cells and their ability to prime naïve T cells. Increasing evidence suggests that maturation stage of DC critically influences the fate of the immune response. Generation of monocyte-derived DC for clinically applicable immunotherapy requires the use of well-defined components and stringent culture conditions. An alternative strategy is to use human autologous serum. However, its constituents are not stable and reflect the inflammatory condition of the donor. In order to investigate whether DC properties are influenced by proteins present in the plasma, we matured human monocyte-derived DC with four main plasma components: fibrinogen, fibronectin, plasminogen or C-reactive protein. These purified proteins were added at various concentrations on day 6 after the initial differentiation induced by IL-4 and GM-CSF. The maturation was assessed by phenotyping of maturation-associated marker (CD83) and co-stimulatory molecule CD86 as well as IL-12 production. Functional properties of DC were assessed by endocytic activity and mixed leukocyte culture. Our results indicate that fibrinogen had DC-maturation effect comparable to poly-I:C, TNF-alpha and PGE(2) as a positive control, but it failed to induce IL-12 production. The other plasma proteins had no effect on DC maturation. CRP at high concentration had rather inhibitory effect on DC induced lymphocyte function. We conclude that none of the tested plasma components and acute phase proteins sufficiently induce fully competent mature DC. This finding is important for the preparation of human DC-based vaccines supplemented by autologous sera.

Natural killer activity of human blood lymphocytes.

Natural killer (NK) activity is an operational designation. It implies the in vitro cytotoxicities registered in short-term tests exerted by lymphocytes derived from donors with no known immunization history against the particular target. The strength of the effect exerted by unmanipulated blood lymphocytes shows an individual variation. Short-term in vitro treatment with interferon elevates the lytic potential of lymphocytes. Owing to the heterogeneity of the cytotoxic blood lymphocytes with regard of cell surface properties it is not possible to separate all active cells and inactive cells in clean populations. A considerable enrichment of active cells can be achieved if nylon wool non-adherent, large, granular Fc gamma receptor positive SRBC receptor negative--or low-avidity SRBC receptor positive--OKM1-reactive cells are separated. Negative cells are concentrated in the Fc receptor and OKM1-negative high-avidity SRBC receptor positive high cell density subset. The activity of lymphocytes in the former category is potentiated by interferon and the latter acquire the lytic function if PHA is added to the assay system. Freshly separated, non-cultured tumor cells are not or weakly sensitive to the effect of unmanipulated lymphocytes. However, when the lymphocytes are treated with interferon prior to the assay a lytic potential can be induced even against these in allogeneic effector target combinations. Cytotoxic cells which acquired the function after in vivo and/or in vitro immunization are designated as 'cytotoxic T-lymphocytes' (CTL), and were shown to act on the basis of antigen recognition. The expression of known T-markers on at least a fraction of the active cells and the recognition of alloantigens in NK systems suggest that the distinction between CTL and NK cells is not as sharp as initially suggested.

Disease-related differences in antibody patterns against EBV-encoded nuclear antigens EBNA 1, EBNA 2 and EBNA 6.

Antibodies to Epstein-Barr virus (EBV) nuclear antigen family (EBNA) and three of its individual members, EBNA 1, EBNA 2 (A and B) and EBNA 6, were measured by anticomplement immunofluorescence (ACIF) in sera of 75 healthy controls, 13 patients with chronic EBV infection, 38 with non-Hodgkin lymphoma (NHL), 23 with Hodgkin's disease (HD), 105 with nasopharyngeal carcinoma (NPC) and 7 patients with infectious mononucleosis (IM). Their anti-EBV lytic antigens were also measured. We observed that: (1) anti-EBNA 2A and E6 rose in parallel 4-6 weeks after IM, followed by anti-EBNA 1 at 3-6 months, (2) all seropositive individuals had anti-EBNA 1; 74% also had anti-EBNA 2A and E6, (3) anti-EBNA 1 accounted for most of the anti-EBNA reactivity in non-IM sera. Striking disease-associated differences were noted on the humoral responses to the lytic and transformation-associated antigens. Compared to the controls, anti-EBNA 1, -EBNA 2A and -EBNA 6 were simultaneously four to 10 times higher in chronic reactivations, whereas only anti-EBNA 1 was elevated (10 times) in NPC. Individual EBNA titres were normal in NHL or HD patients.

Comparison of highly NK active human lymphocyte subsets separated by various procedures involving E, EA rosetting, density gradients and adherence to immune complexes.

Lymphocyte subsets from human blood obtained by different procedures were analyzed for cytotoxic potential and phenotypic characteristics. Nylon wool column passed lymphocytes were fractionated on the basis of: (1) E and Fc gamma receptor expression, (2) cell density and Fc gamma receptor expression, (3) Fc gamma receptor expression. The cytotoxic subsets obtained by separation on the basis of E and EA rosetting differed in their phenotypic composition from those separated on the basis of density or on immune complex monolayers. The E- Fc gamma- population contained few LGL and OKM1 positive cells. The E- Fc gamma+ population was made up almost entirely of LGL and OKM1 positive cells. The low density population was highly enriched in LGLs; among these the Fc gamma- cells were OKT3 positive. In contrast to the E- population the low dense Fc gamma+ cells were mainly LGLs and were OKM1 positive. Fc gamma+ subsets had less killer activity against Daudi cells. The choice of procedure for obtaining a strongly cytotoxic population depends on the needs of particular experiments. Separation on the basis of E rosetting gave lower cell (62%) and cytotoxic (43%) recovery and required about twice the amount of blood and twice the time, as compared with the other 2 procedures. The cell fractions obtained this way allowed characterization of several phenotypically different active populations and showed a difference in cytotoxic potential against K562 and Daudi cells. Density fractionation isolated a highly cytotoxic subset with LGL morphology but this population was still heterogeneous phenotypically. With regard to enrichment of NK activity, the immune complex monolayer attachment method was the most efficient for total cell recovery and for the time taken to perform it.

Leukocyte migration inhibitory factor production by activated lymphocytes representing immunological memory or virus-receptor interaction: response of T cell subsets to Epstein-Barr virus nuclear antigen, response of B cells to UV inactivated Epstein-Barr virus.

Both T and B lymphocytes are known to produce leukocyte migration inhibitory factor (LIF) after appropriate activation. We showed that EBV nuclear antigen (EBNA) triggered T cells for LIF production in an immunologically specific way: only T cells of seropositive individuals responded. Both Fc receptor positive and negative T cells produced LIF, and the presence of macrophages was necessary. The virus itself activated B cells independently of the serological status of the donors, thus the function was not based on immunological memory. This phenomenon was independent of the transforming capacity of the virus, because UV-inactivated virus also elicited LIF production by B lymphocytes. This triggering seems to be the consequence of the virus-receptor interaction on the cell surface.

Clinical status of monoclonal antibodies in the treatment of colorectal carcinoma.

MoABs have demonstrated an antitumor effect and, in time, may lead to improved outcome in patients with colorectal cancer. The authors describe their experience in Sweden and summarize the results of other studies. Primarily, unconjugated mouse MoABs have been used--directed against tumor-associated antigens. More promising are hybrid antibodies composed of mouse and human elements (chimeric), or human MoABs. Such antibodies also can be used as carriers of a cytotoxic compound. The authors discuss two mechanisms by which MoABs induce their antitumor effect, and how cytokines combined with a MoAB can contribute to lysis. The potential roles of anti-idiotypic antibodies are outlined and the use of MoABs postoperatively is proposed.