Tumor antigens known to be immunogenic in man

Immune precision medicine for cancer: a novel insight based on the efficiency of immune effector cells

Cancer cell growth is associated with immune surveillance failure. Nowadays, restoring the desired immune response against cancer cells remains a major therapeutic strategy. Due to the recent advances in biological knowledge, efficient therapeutic tools have been developed to support the best bio-clinical approaches for immune precision therapy. One of the most important successes in immune therapy is represented by the applicational use of monoclonal antibodies, particularly the use of rituximab for B-cell lymphoproliferative disorders. More recently, other monoclonal antibodies have been developed, to inhibit immune checkpoints within the tumor microenvironment that limit immune suppression, or to enhance some immune functions with immune adjuvants through different targets such as Toll-receptor agonists. The aim is to inhibit cancer proliferation by the diminishing/elimination of cancer residual cells and clinically improving the response duration with no or few adverse effects. This effect is supported by enhancing the number, functions, and activity of the immune effector cells, including the natural killer (NK) lymphocytes, NKT-lymphocytes, γδ T-lymphocytes, cytotoxic T-lymphocytes, directly or indirectly through vaccines particularly with neoantigens, and by lowering the functions of the immune suppressive cells. Beyond these new therapeutics and their personalized usage, new considerations have to be taken into account, such as epigenetic regulation particularly from microbiota, evaluation of transversal functions, particularly cellular metabolism, and consideration to the clinical consequences at the body level. The aim of this review is to discuss some practical aspects of immune therapy, giving to clinicians the concept of immune effector cells balancing between control and tolerance. Immunological precision medicine is a combination of modern biological knowledge and clinical therapeutic decisions in a global vision of the patient.

Phage-display selection of a human single-chain fv antibody highly specific for melanoma and breast cancer cells using a chemoenzymatically synthesized G(M3)-carbohydrate antigen

Overexpression of the cell-surface glycosphingolipid G(M3) is associated with a number of different cancers, including those of the skin, colon, breast, and lung. Antibodies against the G(M3) epitope have potential application as therapeutic agents in the treatment of these cancers. We describe the chemoenzymatic synthesis of two G(M3)-derived reagents and their use in the panning of a phage-displayed human single-chain Fv (scFv) antibody library derived from the blood of cancer patients. Three scFv-phage clones, GM3A6, GM3A8, and GM3A15, were selected for recombinant expression and were characterized using BIAcore and flow cytometry. BIAcore measurements using the purified, soluble scFvs yielded dissociation constants (K(d)) ranging from 4.2 x 10(-7) to 2.1 x 10(-5) M. Flow cytometry was used to evaluate the ability of each scFv to discriminate between normal human cells (human dermal fibroblast, HDFa), melanoma cells (HMV-1, M21, and C-8161), and breast cancer cells (BCM-1, BCM-2, and BMS). GM3A6 displayed cross-reactivity with normal cells, as well as tumor cells, and GM3A15 possessed little or no binding activity toward any of the cell lines tested. However, GM3A8 bound to five of the six tumor cell lines and showed no measurable reactivity against the HDFa cells. Hence, we have demonstrated that a synthetic G(M3) panning reagent can be used to isolate a fully human scFv that is highly specific for native G(M3) on the surface of tumor cells. The result is a significant step toward effective immunotherapies for the treatment of cancer.

Resistance of cancer cells to immune recognition and killing

It is well recognized that, in order for a wound to heal, the fibrin clot must be eliminated by fibrinolytic enzymes. In certain instances, however, fibrin is ineffectively degraded or even not degraded. For example, in pregnancy, the placenta contains a layer of fibrin (Nitabuck's layer) which presents as 'self' to the immune system. Similar situations have been observed in many solid tumors. A hypothesis is presented according to which tumor cells can escape detection and attack by the immune system in most cancer patients. The tumor dons a 'coat' of the host's own protein on its cell surface. The coat is composed of fibrin and of a polymeric form of human serum albumin (HSA) which, by contrast to pure fibrin, is resistant to fibrinolytic degradation. Such a coated tumor appears as 'self' to the immune system, and thus is not detected as a tumor by the immune system (i.e. natural killer cells). When tumors are prepared for in vitro assays against drugs, they are routinely treated with proteolytic enzymes (e.g. pepsin, or chymotrypsin, etc.) which dissolve the protein coat, exposing the tumor cell surface to the drug. Thus, the in vivo existence of a coat on the tumor surface may explain why some drugs have little or no effect in vivo, while the same drugs are active in vitro.

Phage-display library selection of high-affinity human single-chain antibodies to tumor-associated carbohydrate antigens sialyl Lewisx and Lewisx

mAbs against tumor-associated carbohydrate antigens have the potential to play a prominent role in cancer immunotherapy. However, it has not been possible to fully exploit the clinical utility of such antibodies primarily, because those of adequate affinity could be derived only from murine sources. To address this problem, we prepared a single-chain Fv (scFv) antibody library from the peripheral blood lymphocytes of 20 patients with various cancer diseases. Completely human high-affinity scFv antibodies were then selected by using synthetic sialyl Lewisx and Lewisx BSA conjugates. These human scFv antibodies were specific for sialyl Lewisx and Lewisx, as demonstrated by ELISA, BIAcore, and flow cytometry binding to the cell surface of pancreatic adenocarcinoma cells. Nucleotide sequencing revealed that at least four unique scFv genes were obtained. The Kd values ranged from 1.1 to 6.2 x 10(-7) M that were comparable to the affinities of mAbs derived from the secondary immune response. These antibodies could be valuable reagents for probing the structure and function of carbohydrate antigens and in the treatment of human tumor diseases.

MNNG-transformed Bloom syndrome B-lymphoblastoids for the detection of Hodgkin's lymphoma-associated antigen in 2D Westerns

Twenty-four hour MNNG-exposed Bloom syndrome (BS) B-lymphoblastoid cells with the potential to form single cell colonies in soft agar and nude mouse tumour (2/6 (33%) showed a simultaneous increase in the Ras-expressing cells (using monoclonal antibody to p21 transforming protein) from 20% (at 24 h) to 85% (on day 30). In contrast, there was an absence of Ras-positive cells in MNNG-exposed fresh lymphocytes (PBMCs) from a healthy subject and a presence of only 11-18% of Ras-positive cells in normal (GA3) and unexposed BS B-lymphoblastoid cells. The Western blot analysis using sera samples from Hodgkin's lymphoma patients showed the presence of proteins of 102 and 68 kDa which in 2D Westerns were observed to be unique to BS-MNNG cells with approximate pIs of 5.3 and 5.7, respectively. It is proposed that BS-MNNG cells provide an interesting in vitro human cell model to generate unique cancer-associated antigen(s) in addition to using this system to understand the primary events associated with neoplastic transformation.

Identification of melanoma antigens that are immunogenic in humans and expressed in vivo

BACKGROUND

In the development of an antimelanoma vaccine, a critical factor is the identification of antigens that induce a strong immune response in humans and that are expressed by melanoma cells in vivo. The aim of this study was to identify candidate antigens for such vaccine.

METHODS

Sixty-nine patients with surgically resected melanomas (American Joint Commission on Cancer [AJCC] stage III) were immunized with a polyvalent vaccine containing multiple melanoma antigens. Antimelanoma antibodies generated in the patients' sera were used as probes to identify the melanoma antigens that are immunogenic in humans and that are expressed on the tumor tissue in vivo. Such responses were determined by an immunoblotting assay that employed an antigen source prepared from membrane fractions of freshly excised melanoma tissue.

RESULTS AND CONCLUSIONS

Vaccine treatment stimulated antibody responses in 35 (51%; 95% confidence interval [CI] = 39%-63%) of 69 sequentially enrolled patients. The antibodies were directed to one or more antigens with molecular masses of 45, 59, 68, 79, 89, 95, and/or 110 kd. The most immunogenic antigens were p110 and p68, which induced responses in 33% (95% CI = 22%-44%) and 25% (95% CI = 15%-35%) of patients, respectively. Both antigens were commonly expressed on different melanomas, but they were absent on autologous normal tissue and on an unrelated allogeneic tumor. All the above antigens are attractive candidates for vaccine construction.

Glycosphingolipid antigens and cancer therapy

Specific types of glycosphingolipid (GSL), which are chemically detectable in normal cells, are more highly expressed in tumors. The high level of expression on the surfaces of tumor cells causes an antibody response to these GSLs, which can therefore be described as tumor-associated antigens. Some of these GSLs have been shown to be adhesion molecules involved in tumor cell metastasis, and to be modulators of signal transduction controlling tumor cell growth and motility. Tumor-associated GSL antigens have been used in the development of antitumor vaccines. GSLs and sphingolipids involved in adhesion and signaling are therefore targets for cancer therapy.

False tumor-positive lymph nodes in radioimmunodiagnosis and radioimmunoguided surgery: etiologic mechanisms

We investigated the causes of false-positive (nontumor cell) focal uptake in radioimmunodiagnosis (RAID) and false-positive high counts in radioimmunoguided surgery (RIGS). Tissue blocks of two such RAID cases were recut and examined by immunohistochemistry (IH) (group 1). Lymph nodes in the drainage area of 14 colon cancers selected because of tumor-positive draining nodes were examined similarly (group 2). The lymph nodes in group 1 showed nontumor cell germinal center (GC) and rare macrophage (M phi) positivity with monoclonal antibody (mAb) CC49 to tumor antigen (Ag) TAG-72, the same Ag to which the mAb B72.3, used for the RAID studies, was directed. In group 2, CC49 staining was observed in the colon cancers, in noncellular tumor Ag in lymphatic channels, and in the GC of draining nodes in a pattern similar to that of follicular dendritic cells (FDC). An In-111-mAb/tumor Ag (TAG-72 or CEA) complex can result in false-positive RAID/RIGS studies by In-111 retained in the lysosomes of lymph node M phi, following attachment of the mAb to the Ag, and their catabolism in the M phi. An I-125-mAb to either tumor Ag could lead to false positive RIGS studies due to its attachment to the Ag portion of ag/ab complexes affixed to the FDC in the GC of the lymph nodes draining a tumor.

Generation of human monoclonal antibodies against ganglioside antigens and their applications in the diagnosis and therapy of cancer

Different approaches to generating human monoclonal antibodies (MAbs) against tumor-associated ganglioside antigens have been carried out in several laboratories. A specific goal addressed by our laboratory is to produce human MAbs to several ganglioside antigens of relevance as therapeutic targets, such as the GM2, GD2, GD3 and GM3 gangliosides in melanoma. In vitro immunization of human B lymphocytes from normal donors was performed using liposomes containing gangliosides as the immunizing antigen combined with either complete tetanus toxoid or a synthetic peptide corresponding to a T helper epitope to stimulate in vitro immunization. Specific human anti-ganglioside antibodies were obtained, indicating that the antibody response found in vitro was antigen-driven. To overcome the widely reported problems concerning stability of immunoglobulin production by the antibody-secreting cell lines, a method of positive selection using GM3-coated magnetic beads has been developed in order to rescue unstable clones. Development of new methods to reproducibly generate ganglioside-specific human MAbs will amplify the possibilities for diagnostic and therapeutic applications.

Anti-melanoma antibodies from melanoma patients immunized with genetically modified autologous tumor cells: selection of specific antibodies from single-chain Fv fusion phage libraries

Fusion phage libraries expressing single-chain Fv antibodies were constructed from the peripheral blood lymphocytes of two melanoma patients who had been immunized with autologous melanoma cells transduced the gamma-interferon gene to enhance immunogenicity, in a trial conducted at another institution. Anti-melanoma antibodies were selected from each library by panning the phage against live cultures of the autologous tumor. After two or three rounds of panning, clones of the phage were tested by ELISA for binding to the autologous tumor cells; > 90% of the clones tested showed a strong ELISA reaction, demonstrating the effectiveness of the panning procedure for selecting antimelanoma antibodies. The panned phage population was extensively absorbed against normal melanocytes to enrich for antibodies that react with melanoma cells but not with melanocytes. The unabsorbed phage were cloned, and the specificities of the expressed antibodies were individually tested by ELISA with a panel of cultured human cells. The first tests were done with normal endothelial and fibroblast cells to identify antibodies that do not react, or react weakly, with two normal cell types, indicating some degree of specificity for melanoma cells. The proportion of phage clones expressing such antibodies was approximately 1%. Those phage were further tested by ELISA with melanocytes, several melanoma lines, and eight other tumor lines, including a glioma line derived from glial cells that share a common lineage with melanocytes. The ELISA tests identified three classes of anti-melanoma antibodies, as follows: (i) a melanoma-specific class that reacts almost exclusively with the melanoma lines; (ii) a tumor-specific class that reacts with melanoma and other tumor lines but does not react with the normal melanocyte, endothelial and fibroblast cells; and (iii) a lineage-specific class that reacts with the melanoma lines, melanocytes, and the glioma line but does not react with the other lines. These are rare classes from the immunized patients' repertoires of anti-melanoma antibodies, most of which are relatively nonspecific anti-self antibodies. The melanoma-specific class was isolated from one patient, and the lineage-specific class was isolated from the other patient, indicating that different patients can have markedly different responses to the same immunization protocol. The procedures described here can be used to screen the antibody repertoire of any person with cancer, providing access to an enormous untapped pool of human monoclonal anti-tumor antibodies with clinical and research potential.