Redirecting T cells to eradicate B-cell acute lymphoblastic leukemia: bispecific T-cell engagers and chimeric antigen receptors.

Recent advances in antibody technology to harness T cells for cancer immunotherapy, particularly in the difficult-to-treat setting of relapsed/refractory acute lymphoblastic leukemia (r/r ALL), have led to innovative methods for directing cytotoxic T cells to specific surface antigens on cancer cells. One approach involves administration of soluble bispecific (or dual-affinity) antibody-based constructs that temporarily bridge T cells and cancer cells. Another approach infuses ex vivo-engineered T cells that express a surface plasma membrane-inserted antibody construct called a chimeric antigen receptor (CAR). Both bispecific antibodies and CARs circumvent natural target cell recognition by creating a physical connection between cytotoxic T cells and target cancer cells to activate a cytolysis signaling pathway; this connection allows essentially all cytotoxic T cells in a patient to be engaged because typical tumor cell resistance mechanisms (such as T-cell receptor specificity, antigen processing and presentation, and major histocompatibility complex context) are bypassed. Both the bispecific T-cell engager (BiTE) antibody construct blinatumomab and CD19-CARs are immunotherapies that have yielded encouraging remission rates in CD19-positive r/r ALL, suggesting that they might serve as definitive treatments or bridging therapies to allogeneic hematopoietic cell transplantation. With the introduction of these immunotherapies, new challenges arise related to unique toxicities and distinctive pathways of resistance. An increasing body of knowledge is being accumulated on how to predict, prevent, and manage such toxicities, which will help to better stratify patient risk and tailor treatments to minimize severe adverse events. A deeper understanding of the precise mechanisms of action and immune resistance, interaction with other novel agents in potential combinations, and optimization in the manufacturing process will help to advance immunotherapy outcomes in the r/r ALL setting.

Combined automated cell and flow cytometric analysis enables recognition of persistent polyclonal B-cell lymphocytosis (PPBL), a study of 25 patients.

Persistent polyclonal B-cell lymphocytosis (PPBL) is an extremely rare disorder, which occurs almost exclusively in smoking women and is characterized by a lymphocytosis with circulating binucleated lymphocytes. We analyzed 25 PPBL patients with respect to immunophenotype and by adaptive cluster analysis system (ACAS). Furthermore, HLA type, presence of Epstein-Barr virus (EBV) DNA in B cells, and clinical data were evaluated. Overall, the median percentages of B cells in PPBL patients with expression of CD5(dim), CD23(dim), CD25, CD27, and FMC7 were 21%, 38%, 16%, 74%, and 93%. Compared to normal controls, ACAS revealed a subset of nucleic-acid-rich lymphocytes located between the regular lymphocyte and regular monocyte region. Sixteen (64%) of 25 patients carried a HLA DR7 phenotype. Quantitative real-time polymerase chain reaction analysis did not detect relevant amounts of EBV DNA in circulating B cells of any patient. During a median follow-up of 5 years, a single patient developed lymphoplasmacytic lymphoma. The abnormal morphology and frequent, albeit dim, expression of CD5 and CD23 in PPBL may result in erratic diagnostic assignment of this benign disorder. However, incorporation of immunophenotyping and ACAS into the diagnostic algorithm allows recognition of PPBL in routine analysis and its differentiation from malignant B cell lymphoproliferative diseases. We found that an infection of a significant percentage of PPBL cells by EBV is unlikely. The observation of malignant lymphoma in a single patient implicates that evolution into a clonal malignant transformation may occasionally occur in PPBL.

Increased chondroitin sulphate proteoglycan expression (B5 immunoreactivity) in metastases of uveal melanoma.

BACKGROUND: Metastatic uveal melanoma has a poor prognosis and limited therapeutic options. Proteoglycans are involved in tumor cell invasion and metastatic behavior. The mAbB5 stains a chondroitin sulphate proteoglycan (CSPG) on cutaneous melanoma cells. Here, we compare the B5-staining of CSPG in primaries and metastases of uveal melanoma. MATERIAL AND METHODS: Immunohistopathological staining was performed in 15 cutaneous and 39 uveal melanoma samples. A score for intracellular and surface staining was established. B5 staining was compared in primaries and metastases of uveal melanoma using Student's t-test. RESULTS: Eight of 11 (73%) uveal melanoma metastases were positive for B5-staining whereas only 5 of 28 (18%) primary uveal melanoma samples were B5-positive (P < 0.001). Nine of 15 cutaneous melanoma samples (60%) were B5-positive without significant difference between primary and metastatic lesions. Surface staining was found both on uveal melanoma metastases and cutaneous melanomas. CONCLUSIONS: CSPG was expressed significantly more often in metastases than in primaries of uveal melanoma. It potentially may be one factor associated with metastatic spread. Further studies are needed to determine its use as prognostic factor. The mAbB5 may also be a promising tool for immunotherapy due to its strong staining of CSPG on the surface of cutaneous and metastatic uveal melanoma cells.

Biased epitope selection by recombinant vaccinia-virus (rVV)-infected mature or immature dendritic cells.

Recombinant expression vectors represent a powerful way to deliver whole antigens (Ags) for immunization. Sustained Ag expression in vector-infected dendritic cells (DC) combines Ag-specific stimulation with powerful costimulation and, simultaneously, through 'self-selection' of ad hoc epitopes broadens the scope of immunization beyond restrictions posed by individual patients' human leukocyte antigen (HLA) phenotype. In this study, therefore, we evaluated the efficiency of a recombinant vaccinia virus encoding the gp100/PMel17 melanoma Ag (rVV-gp100) to infect immature (iDC) or mature dendritic cells (mDC) derived from circulating mononuclear cells and the effect of infection on their status of maturation. In addition, we tested the ability of rVV-gp100-infected iDC and mDC to present the HLA-A*0201-associated gp100:209-217 epitope (g209). Irrespective of status of maturation, rVV-gp100 infection induced gp100 expression while only partially reversing the expression of some maturation markers. However, endogenous presentation of the wild-type g209 epitope was inefficient. The low efficiency was epitope-specific since infection of DC with rVV encoding a gp100 construct containing the modified gp100:209-217 (210M) (g209-2M) epitope characterized by high binding affinity for HLA-A*0201 restored efficient Ag presentation. Presentation of an HLA-class II-associated epitope and cytokine release by DC was not altered by rVV infection. Thus, Ag expression driven by rVV may be an efficient strategy for whole Ag delivery. However, since the effectiveness of Ag processing and presentation is subject to stringent HLA/epitope pairing, and for other yet undefined rules, the assumption that whole Ag delivery may circumvent HLA restriction is incorrect and recombinant expression vectors encoding well-characterized polyepitopic constructs may prove more effective.

Natural T-cell response against MHC class I epitopes of epithelial cell adhesion molecule, her-2/neu, and carcinoembryonic antigen in patients with colorectal cancer.

The antigens epithelial cell adhesion molecule (Ep-CAM), her-2/neu, and carcinoembryonic antigen (CEA) are potential T-cell targets in antigen-specific vaccination-based cancer therapy. We performed this study to evaluate whether a natural specific T-cell response against these tumor-associated antigens (TAAs) already exists in patients with colorectal carcinoma (CRC). We used the IFN-gamma ELISPOT assay to detect circulating TAA-reactive T cells directly ex vivo in unstimulated peripheral blood mononuclear cells. We analyzed the T-cell response in peripheral blood mononuclear cells of 22 HLA-A2-positive patients with CRC and 8 HLA-A2-positive healthy subjects against 3 HLA A2-restricted peptide epitopes of the TAAs Ep-CAM (GLKAGVIAV), her-2/neu (IISAVVGIL), and CEA (YLSGANLNL). Seven of 22 patients but none of the 8 healthy subjects had T cells specifically secreting IFN-gamma in response to one to three of these antigens (n = 4, Ep-CAM; n = 5, her-2/neu; n = 6, CEA). In three of the seven responding patients, TAA-reactive T cells were further characterized by flow cytometry. In all three patients, the majority of these T cells have a CD3+CD8+IFN-gamma+CD69+CD45RA+ phenotype, resembling activated effector-type T cells. T-cell responses occurred only in patients with metastatic disease (Dukes' stages C and D). The results of this study indicate that natural T-cell responses against TAAs occur in approximately one-half of CRC patients with involvement of lymph nodes or distant metastases, but not in CRC patients with disease confined to the intestinum.

High frequencies of circulating melanoma-reactive CD8+ T cells in patients with advanced melanoma.

To determine whether circulating tumor-reactive T cells are present in melanoma patients, unstimulated T cells from peripheral blood were tested for recognition of HLA-A2- or HLA-A1-matched melanoma cell lines using the ELISPOT assay. Eleven out of 19 patients with metastatic melanoma had a T-cell response with up to 0.81%, 0.78%, 0. 53%, 0.12%, 0.10%, 0.09%, 0.07%, 0.06%, 0.06%, 0.04%, and 0.04% of peripheral blood mononuclear cells (PBMC) secreting IFNgamma upon exposure to various HLA-A2- or HLA-A1-matched melanoma cell lines. These T-cell responses were mediated by CD8+ T cells and could specifically be blocked by an anti-HLA-A2 antibody in HLA-A2-positive patients. Separation experiments performed in one melanoma patient showed tumor-reactive T cells in both the CD8+ effector T cell (CD45RA+/IFNgamma+) as well as the CD8+ memory T-cell compartment (CD45RO+/IFNgamma+). In 3 out of 5 patients, in whom autologous cell lines were available, similar frequencies of T cells in response to HLA-A1- or HLA-A2-matched allogeneic and autologous tumor cells were observed, while 2 patients had a T-cell response restricted to either the autologous or the allogeneic cell lines. These results give evidence for the presence of tumor-reactive CD8+ T cells in more than half of melanoma patients tested. Although some of these patients have clinical evidence for an immunological-mediated tumor control, several patients have growing tumors suggesting presence of escape mechanisms.