Cancer immunotherapy: synthetic and natural peptides in the balance

The identification of human tumor-associated antigens has opened new avenues for immune intervention in cancer. Clinical trials using synthetic peptides that match segments of known tumor-associated proteins are ongoing. Alternatively, naturally processed peptides, obtained by acid treatment of tumor cells can be used. Here, Matteo Bellone and colleagues discuss the advantages and disadvantages of synthetic versus natural tumor peptides in cancer immunotherapy.

Blockade of the Fas-triggered intracellular signaling pathway in human melanomas is circumvented by cytotoxic lymphocytes

Fas and Fas ligand (FasL) have been found both in lymphoid and in non-lymphoid malignancies, and are thought to play a role in the interplay between tumors and the immune system. Here we investigated Fas/FasL expression, function and intracellular signalling pathways in human melanomas. Of 5 melanoma cell lines, 3 expressed Fas at their surface, and all of them expressed FasL. FasL was functional, since it triggered Fas-induced apoptosis of human T lymphocytes clones. Conversely, cross-linking of Fas molecule with a specific monoclonal antibody failed to induce apoptosis in any of the melanomas tested, or ceramide intracellular accumulation or caspase-3 activation, pointing to an early alteration in the Fas-triggered signaling cascade. All melanomas retained the ability to undergo apoptosis induced by cytotoxic lymphocytes, which was mediated by the granule exocytosis mechanism. This suggests that melanoma cells evade immune-mediated Fas-triggered apoptosis via a selective blockade of the Fas apoptotic pathway. Cytotoxic lymphocytes, however, may circumvent tumor resistance to Fas-induced death via granzyme-mediated apoptosis, further supporting the development of immunotherapeutic strategies in the treatment of cancer.

Major histocompatibility complex class I restricted cytotoxic T cells specific for natural melanoma peptides recognize unidentified shared melanoma antigen(s)

CTLs were generated in vitro from two healthy donors and one melanoma patient by stimulation of CD8+ T cells with autologous dendritic cells pulsed with natural melanoma peptides (NMPs), obtained by acid treatment of HLA-matched melanoma cells. CTLs showed MHC class I-restricted melanoma-specific cytolytic activity. Importantly, CTLs from the patient, induced with NMPs obtained from an allogeneic HLA-A-matched melanoma, killed the autologous tumor. COS-7 cells cotransfected with the cDNA of 13 melanoma antigens and the HLA-A1-restricting allele did not induce cytokines release from NMP-specific CTLs, suggesting that they recognize unidentified shared melanoma antigens and that they may be valuable for identification of new tumor antigens. These results strongly support the use of autologous and/or allogeneic NMP-pulsed dendritic cells as cancer vaccines in patients whose neoplasms do not express or have lost expression of known tumor antigens.

Melanoma cells present a MAGE-3 epitope to CD4(+) cytotoxic T cells in association with histocompatibility leukocyte antigen DR11

In this study we used TEPITOPE, a new epitope prediction software, to identify sequence segments on the MAGE-3 protein with promiscuous binding to histocompatibility leukocyte antigen (HLA)-DR molecules. Synthetic peptides corresponding to the identified sequences were synthesized and used to propagate CD4(+) T cells from the blood of a healthy donor. CD4(+) T cells strongly recognized MAGE-3281-295 and, to a lesser extent, MAGE-3141-155 and MAGE-3146-160. Moreover, CD4(+) T cells proliferated in the presence of recombinant MAGE-3 after processing and presentation by autologous antigen presenting cells, demonstrating that the MAGE-3 epitopes recognized are naturally processed. CD4(+) T cells, mostly of the T helper 1 type, showed specific lytic activity against HLA-DR11/MAGE-3-positive melanoma cells. Cold target inhibition experiments demonstrated indeed that the CD4(+) T cells recognized MAGE-3281-295 in association with HLA-DR11 on melanoma cells. This is the first evidence that a tumor-specific shared antigen forms CD4(+) T cell epitopes. Furthermore, we validated the use of algorithms for the prediction of promiscuous CD4(+) T cell epitopes, thus opening the possibility of wide application to other tumor-associated antigens. These results have direct implications for cancer immunotherapy in the design of peptide-based vaccines with tumor-specific CD4(+) T cell epitopes.

Human melanoma cells transfected with the B7-2 co-stimulatory molecule induce tumor-specific CD8+ cytotoxic T lymphocytes in vitro

Neoplastic cells express tumor-associated antigens, but tumor rejection seldom occurs in vivo. The absence of an effective immune response may be explained by the inability of tumor cells to deliver co-stimulatory signals. Indeed, transfection of either B7-1 or B7-2 co-stimulatory molecules into mouse tumor cells enhances antitumor immune responses. In this study, we stably transfected human melanoma cells with the cDNA encoding the B7-2 molecule to evaluate in vitro: (i) the induction of anti-melanoma cytotoxic T lymphocytes (CTL) by stimulation of CD8+ T cells, purified from healthy donors and a melanoma patient, with B7-2 transfected allogeneic HLA-matched melanoma cells; (ii) the tumor specificity and the HLA restriction of the induced CTL; and (iii) the feasibility to propagate long-term antimelanoma CTL lines. We found that B7-2 transfected, but not untransfected or mock-transfected, melanoma cells activated MHC-class I-restricted, melanoma-specific CD8+ CTL from healthy donors. More importantly, CD8+ tumor-associated lymphocytes, purified from a tumor-invaded lymph node of a melanoma patient and stimulated with B7-2-transfected melanoma cells, acquired a strong reactivity toward the autologous tumor. CTL lines with specific cytolytic activity could be propagated in long-term culture. These results indicate that: (i) the expression of the B7-2 molecule into human melanoma cells makes them immunogenic and able to act as antigen-presenting cells and (ii) purified CD8+ cells, stimulated with B7-2+ allogeneic HLA-matched melanoma cells, preferentially recognize melanoma-specific rather than allogeneic antigens. This study may have clinical implications for passive and/or active immunotherapy in melanoma patients.

Anti-CD4 monoclonal antibody (mAb) and anti-idiotypic mAb to anti-CD4 in the therapy of autoimmune diseases

The present report critically reviews the rationale, experimental and clinical effectiveness and limits of anti-CD4 monoclonal antibody (mAb) therapy. References are also made to a novel approach involving active immunotherapy and an anti-idiotypic mAb bearing the internal image of human CD4 antigen. Preliminary observations concerning the effects of this treatment in one patient with rheumatoid arthritis and in one patient with systemic lupus erythematosus are reported.

dsDNA-, nucleohistone- and DNASE I-reactive T lymphocytes in patients affected by systemic lupus erythematosus: correlation with clinical disease activity

OBJECTIVE

To demonstrate the involvement of T lymphocytes reactive to autoantigens in the pathogenesis of autoimmune diseases and to analyse their clinical relevance.

METHODS

The frequency of T cell clones reactive to double strand DNA (dsDNA), Nucleohistone (NH) complex and Dnase I was calculated for the peripheral blood mononuclear cells (PBMC) of 15 SLE patients and 9 healthy subjects by proliferation assay.

RESULTS

DsDNA- and NH-specific T cell clones were found in the majority of the patients analysed (frequency ranging from 2 to 50 clones/10(7) PBMC), while their absence or very low frequency (2 clones/10(7) PBMC) was observed in the control PBMC. Their frequency significantly correlated with decreased serum concentrations of C3 and C4 and with the systemic lupus erythematosus disease activity index (P = 0.03). A very low frequency of Dnase I-reactive T cell clones was observed in both SLE and healthy subjects.

CONCLUSION

Our results suggest that dsDNA- and NH-reactive T lymphocytes may be involved in the pathogenesis of SLE and that their quantification in the peripheral blood of patients could be a useful tool to follow the clinical course of the disease.

Human CD4-internal antigen anti-idiotypic monoclonal antibody: induction of a CD4-specific response in humans

We previously showed that anti-idiotypic mAb (mAb2) F16-16D7 (16D7) to the paratope (or paratope-related idiotope) of the anti-CD4 mAb HP2/6 induces anti-CD4 Abs in BALB/c mice. In view of the potential ability of 16D7 to induce anti-CD4 Ab in humans and the potential benefits of anti-CD4 Abs in the treatment of autoimmune diseases, we evaluated the immunologic response to and assessed the safety of four 2-mg 16D7 s.c. injections in one patient with systemic lupus erythematosus (SLE) and one with rheumatoid arthritis (RA). 16D7 induced anti-isotypic and anti-anti-idiotypic Abs (Ab3), which were almost exclusively of the IgG isotype. Ab3 specifically reacted with 16D7 as they inhibited its binding to mAb HP2/6. Although Ab3 did not react with cellular or recombinant CD4 (rCD4), single-cell enzyme-linked immunospot assays of anti-CD4 Ab production revealed many more spot-forming cells in rCD4- and 16D7-coated wells than in wells coated with BSA or 16D7 isotype-matched MK2-23. Spot-forming anti-CD4 Abs were specifically induced by 16D7, since rCD4-dependent spot formation 1) was not observed with PBL from one patient with SLE, one with mixed connective tissue disease, and one with melanoma immunized with MK2-23; and 2) was inhibited by 16D7 and not by MK2-23. Spot-forming anti-CD4 Abs recognize a CD4 epitope identical (or closely related) to that seen by HP2/6, since this specifically inhibited spot formation. A substantial, although transient, CD4+ T cell depletion was only observed in the RA patient. Local and/or general toxicity and laboratory and/or clinical signs indicative of immunodepression or diseases relapse were not observed during an 18-month follow-up.

Human CD4-internal antigen anti-idiotypic monoclonal antibody: induction of a CD4-specific response in humans

We previously showed that anti-idiotypic mAb (mAb2) F16-16D7 (16D7) to the paratope (or paratope-related idiotope) of the anti-CD4 mAb HP2/6 induces anti-CD4 Abs in BALB/c mice. In view of the potential ability of 16D7 to induce anti-CD4 Ab in humans and the potential benefits of anti-CD4 Abs in the treatment of autoimmune diseases, we evaluated the immunologic response to and assessed the safety of four 2-mg 16D7 s.c. injections in one patient with systemic lupus erythematosus (SLE) and one with rheumatoid arthritis (RA). 16D7 induced anti-isotypic and anti-anti-idiotypic Abs (Ab3), which were almost exclusively of the IgG isotype. Ab3 specifically reacted with 16D7 as they inhibited its binding to mAb HP2/6. Although Ab3 did not react with cellular or recombinant CD4 (rCD4), single-cell enzyme-linked immunospot assays of anti-CD4 Ab production revealed many more spot-forming cells in rCD4- and 16D7-coated wells than in wells coated with BSA or 16D7 isotype-matched MK2-23. Spot-forming anti-CD4 Abs were specifically induced by 16D7, since rCD4-dependent spot formation 1) was not observed with PBL from one patient with SLE, one with mixed connective tissue disease, and one with melanoma immunized with MK2-23; and 2) was inhibited by 16D7 and not by MK2-23. Spot-forming anti-CD4 Abs recognize a CD4 epitope identical (or closely related) to that seen by HP2/6, since this specifically inhibited spot formation. A substantial, although transient, CD4+ T cell depletion was only observed in the RA patient. Local and/or general toxicity and laboratory and/or clinical signs indicative of immunodepression or diseases relapse were not observed during an 18-month follow-up.

Particulate naturally processed peptides prime a cytotoxic response against human melanoma in vitro

For an efficient antitumor cytotoxic response, tumor antigenic peptides need to be presented by professional antigen-presenting cells in association with MHC class I molecules. We established in vitro short-term human CTL lines from healthy and melanoma-bearing subjects, using as antigen-presenting cells autologous adherent cells after phagocytosis of latex beads coated with melanoma peptides. Melanoma peptides were obtained by acid extraction of melanoma cells that matched with donor peripheral blood mononuclear cells, at least for one HLA-A allele. The cytotoxic activity of the lines was specific for the melanoma from which peptides were obtained and for melanoma sharing HLA alleles. These results demonstrate that a complex mixture of naturally processed melanoma peptides conjugated to a phagocytic substrate that targets them into the MHC class I pathway of adherent cells can prime a CTL response in healthy subjects in vitro, and that peptides from allogeneic tumors may be used to propagate CTL in melanoma patients. Our data support the feasibility of active and passive vaccination procedures with nonliving vaccines in cancer patients.

IL2 triggers a tumor progression process in a melanoma cell line MELP derived from a patient whose metastasis increased in size during IL2/INFalpha biotherapy

Human melanomas may express both in vivo and in vitro functional IL-Rs and may be expected to directly respond to injected IL2. This may generate biological situations which may be favourable for the patient, but also for tumor progression. Here, we analyse the latter hypothesis. MELP is a melanoma cell line derived from a patient whose metastasis increased in size during IL2/IFN alpha biotherapy [correction of biotheraphy]. These cells have been characterized in vitro for their phenotype and for their sensitivity to IL2. In vitro MELP cells express an IL2-R alpha(+) beta(+) gamma(-) phenotype and IL2 treatment induces the acquisition of new functional characteristics represented (i) by the increased surface expression of two markers of metastatic evolution (ICAM-1 and CD44); (ii) by the stable induction of the IL2-R gamma with the appearance of functional IL2-R beta complex, which are also recognized by GM-CSF; (iii) by the inhibition of transcription of a regulatory cytokine such as IL6; (iv) by a differential effect of IL6 on CD44 surface expression in MELP cells treated or not with IL2 (MILG cells); (v) by the acquisition of faster growth rates and appearance of piling up and multilayer cellular organization; (vi) by the development of rapidly growing tumors in nude mice. IL2 induces in MELP cells a tumor progression process that could mimic the metastatic evolution observed in vivo during biotherapy. Therefore, MELP phenotype may help to define a subset of patients in which IL2 therapy may trigger unfavourable evolution.

CD4+ Th0 cell clones, isolated from a metastatic lymph node of a melanoma patient, possess cytolytic function

In the present study T lymphocytes isolated from a metastatic lymph node (T-LNL) of a melanoma patient have been cloned. In the attempt to verify whether T-LNL may acquire in vitro functional activities in the absence of tumour-associated antigens, they were cloned utilizing allogenic lymphocytes as feeder cells. Nineteen clones generated from T-LNL proved to be CD4+ and, among these, five were able to kill autologous and allogeneic human melanoma cells in HLA-class-II-restricted way. On the basis of their cytokine production, these CD4+ cytolytic T-LNL clones were shown to belong to the Th0 subset and three of them expressed the V beta 17 chain of the T cell receptor. These results suggest the presence of melanoma-specific but functionally inactive lymphocytes with T cell receptor oligoclonality in the lymph node environment. These specific T cells may acquire in vitro the capacity to kill autologous and allogeneic tumours without any induction by autologous melanoma cells.

Increased level of serum HLA class I antigens in HIV infection. Correlation with disease progression

Analysis of (sHLA-I) antigens in a large number of HIV-positive subjects found a significant increase of their level, but did not detect any change in their molecular profile. Monitoring at yearly intervals for four years of the sHLA-I antigen level in 14 HIV-positive subjects with a normal sHLA-I antigen level at study entry showed a significant correlation between progressive increase of sHLA-I antigen level and disease progression. Furthermore, a Kaplan-Meier plot of the frequency of development of AIDS in 34 patients whose cases were followed for 7 years showed that sHLA-I antigen level is a strong predictor of progression to AIDS. Its predictive value is comparable to that of serum beta 2-mu level, greater than that of serum neopterin, and lower than that of CD4+ T-cell percentage. The predictive value of sHLA-I antigen level in combination with serum beta 2-mu level, neopterin level, or CD4+ T-cell percentage is greater than that of each individual variable. These results suggest that measurement of the sHLA-I antigen level may provide useful prognostic information in HIV-positive subjects.

Immune cell circulating subsets are affected by gonadal function

Influence on the immune system activity by sex hormones has been widely reported. Fertile women are proner to the onset of autoimmune diseases than men, but this increased susceptibility disappears after menopause. The hormonal changes are very likely to be responsible for this event, but precise correlations between sex hormone levels and immune functions have not been defined. For this reason we have analyzed phenotype and natural cytotoxicity of peripheral blood lymphocytes (PBL) from 35 women in menopause, comparing them with the same parameters of 28 fertile and 8 postmenopausal women and correlating them with the hormonal pattern of each group. We have also considered 8 women with premature menopause. Hormonal levels have been detected by radioimmune assays, while PBL phenotype has been studied by immunofluorescence and FACS analysis. The natural killer (NK) cell activity has been calculated on the basis of a chromium release assay. Postmenopausal women showed a reduction of the number of total lymphocytes (1650 +/- 215 cells/mmc) in comparison to fertile women (2081 +/- 200 cells/mmc, P < 0.01). The decrease mainly involved B and CD4+ T lymphocyte subpopulations (P < 0.05 and P < 0.01, respectively). Women with premature menopause had lower percentage of CD4 lymphocytes (34% vs 47%, P < 0.01) and higher percentage of CD8 (30% vs 22%, P < 0.02) and NK cells (32% vs 14%, P < 0.009) than fertile women of the same age. The percentage of circulating lymphocytes expressing HLA class II antigens also resulted as being increased (22% vs 9%, P < 0.01). The number of total, CD2, CD4 T lymphocytes, B and NK cells correlated positively with LH and negatively with FSH serum levels (P < 0.05 and P < 0.002, respectively). PRL positively influenced CD2, CD4 and B lymphocyte numbers (P < 0.001). FSH and 17 beta-estradiol inversely affected CD8 and B lymphocyte numbers (P < 0.005 and P < 0.02, respectively). In conclusion, the increase of FSH and the decrease of PRL levels appear to be involved in the reduction of B and CD4 T lymphocytes thus lowering the risk for the onset of autoimmune diseases during and after menopause. Generalized activation of the immune system (raised expression of HLA class II antigens) with elevated numbers of cytotoxic subpopulations (CD8 and NK lymphocytes) is present in women affected by premature menopause suggesting the involvement of autoimmune dysregulation in the pathogenesis of this syndrome.

Immunotherapy with intralesional and systemic interleukin-2 of patients with non-small-cell lung cancer

Eight patients affected by non-small-cell lung cancer were treated with intralesional and systemic recombinant IL-2 (rIL-2) injection with the aim of activating both tumour-infiltrating lymphocytes and circulating cytotoxic or killer cells. The schedule of treatment was as follows: a daily fine-needle transparietal intralesional rIL-2 injection (1 x 10(5) Cetus units) from day 1 to day 5 and systemic rIL-2 infusion (1 x 10(5) Cetus units kg-1 day-1) from day 6 to day 10. One to four cycles of treatment were received by each patient. Clinical and immunological evaluations were performed (a) before treatment, (b) following the intralesional rIL-2 administration, (c) 1 h after the beginning of rIL-2 infusion and (d) at the end of the systemic rIL-2 infusion. No complete remission was achieved, two patients showed a partial remission, three resulted in stable disease and three patients progressed. Natural killer and lymphokine-activated killer cell activity dramatically decreased 1 h after the beginning of rIL-2 infusion and increased at the end of treatment. A progressive increase of circulating CD8+ and HLA class II+ T cells as well as of CD8+ T cell clones, most of which displayed NK activity, was recorded following rIL-2 infusion. Present data indicate that (a) the local administration of rIL-2 coupled with systemic rIL-2 infusion may be suggested as an alternative approach for the immunotherapy of lung cancer, (b) rIL-2 induces different immunological modifications according to the route and the time of its administration and (c) rIL-2 administration increases the amount of circulating immune cells with potential antitumour activity.