Active immunization with a structurally aggregated PD-L1 antigen breaks T and B immune tolerance in non-human primates and exhibits in vivo anti-tumoral effects in immunocompetent mouse tumor models.

Despite the clinical success of the programmed death ligand 1 (PD-L1) blocking therapy in cancer treatment, only a subset of patients exhibits durable responses, therefore further exploration of other immunotherapeutic alternatives are needed. This paper reported the development of the PKPD-L1Vac vaccine, a new protein vaccine candidate that uses aluminum phosphate as an adjuvant and as an antigen the extracellular domain of human PD-L1 fused to a 47 amino-terminal portion of the LpdA protein from N. meningitides (PKPD-L1). The PKPD-L1 antigen has different physical and biological characteristics than those found in the natural molecule and in others PD-L1 vaccine candidates. The quimeric protein has a reduced binding capacity to the PD-1 and CD80 receptors to decrease their pro-tumoral activity. Besides, the distinctive feature of the PKPD-L1 polypeptide to be structurally aggregated could be desirable for its immunogenic properties. PKPD-L1Vac elicited anti-PD-L1-specific IgG antibodies and T lymphocyte-mediated immunity in mice and non-human primates. The vaccine administration demonstrated antitumor activity on CT-26 and B16-F10 primary tumor models in mice. Moreover, the immunization with PKPD-L1Vac increased the tumor-infiltrating lymphocytes and decreased the proportion of CD3+CD8+PD1+high anergic T cells in CT-26 tumor tissues, suggesting that the vaccine may remodel the tumor microenvironment. In summary, the PKPD-L1Vac vaccine exhibits very promising preclinical results and deserves to move forward to a phase I clinical trial.

A point mutation in a murine immunoglobulin V-region strongly influences the antibody yield in Escherichia coli.

Recombinant DNA technology has made it possible to produce specific Fab and scFv antibody (Ab) fragments in prokaryotic host cells. Using vectors designed for periplasmic expression of encoded Ab fragments, we have been studying how the sequence and genetic localization of the light chain (L-chain) variable region gene of a mouse Ab (CB-Nm.1) determined the level of Ab production. The variable region was shown to belong to the V kappa V family and contained a previously unreported Ile72. Nine different Ab constructions were tested in monocistronic (scFv) or dicistronic (Fab) operons for their ability to affect the synthesis level of the L-chain. When the gene coding for the L-chain was located downstream from the Fd fragment gene, the substitution of codons encoding Ile by a codon encoding Thr was found to be crucial for any expression of the L-chain fragment. This was, however, not accompanied by an increase in L-chain-specific mRNA, neither was there any change in the size of the mRNA. The fact that the unmutated L-chain protein was produced from cells transformed with certain other constructions indicated that the protein as such was not incompatible with the prokaryotic environment. Together, this suggested that the translation process was involved in the restricted production of the L-chain. Thus, surprisingly small substitutions significantly affected the expression level, a fact that will have important implications on the library size expressed in prokaryotic hosts, including phage-displayed Ab libraries.

Antibody engineering at the millennium.

It has been almost 100 years since von Behring and Kitasato received the first Nobel prize for the discovery of passive immunotherapy and nearly 25 years since Köhler and Milstein first reported hybridoma technology. In the 15 years since Mullis and co-workers described PCR, a number of discoveries and technologies have converged to produce a renaissance in antibody therapeutics. Our vision of antibodies as tools for research--useful for the prevention, detection and treatment of disease--has been revolutionized by these recent advances. This review specifically focuses on what is now called antibody engineering and includes chimeric and humanized antibodies, immunoglobulin fragments, antibody libraries, antibody fusion proteins and transgenic organisms as bioreactors. As a consequence of refinements in antibody technology, the field of genetically engineered immunoglobulins has matured into an elegant and important drug and reagent development platform.

Bacterial single-chain antibody fragments, specific for carcinoembryonic antigen.

We have produced single-chain antibody (scFv) fragments in bacteria specific for carcinoembryonic antigen (CEA). Polymerase chain reaction (PCR) was used for the cloning and modification of the heavy and light variable regions (VH and VL) of the mouse monoclonal antibody (MAb) CB-CEA.1. A 14-amino acid linker was used in the synthesis of the scFv gene. The VH and VL regions were amplified from cDNA by PCR using 5' end FR1 and 3' end constant region primers, and then sequenced. VH was then amplified by PCR using an exact 5' end FR1 primer, and a phosphorylated (PP) 3' end primer for J2 that also encoded the first 7 amino acids of the linker. VL was amplified with a PP 5' end primer for FR1, also encoding the remaining 7 amino acids of the linker, and a 3' end primer for J5, plus a stop codon and a BglII restriction site. The fragments were ligated and reamplified with the PP VH 5' and VL 3' end primers. The VH-linker-VL structure was blunt-cloned into expression vectors bearing the tryptophan promoter and pelB or ompA signal peptide sequences. Culture supernatant, bacteria pellet and periplasm preparations were assayed in Western blot and a protein of about 27 kDa was identified with rabbit antibodies specific for the Fab of CB-CEA.1. Bacterial supernatant and periplasm preparations also inhibited the recognition of CEA by HRP-labeled CB-CEA.1 in enzyme-linked immunosorbent assay (ELISA). Periplasm preparations were purified by affinity chromatography with specific anti-idiotypic MAbs. The Western blot of the eluates identified a protein of approximately 27 kDa that blocked the recognition of CEA by HRP-labeled CB-CEA.1 in ELISA. The VH-linker-VL structure was cloned into a vector bearing the lacZ promoter and the pelB signal peptide. The recombinant bacterial clones also expressed about 27 kDa scFv, specific for CEA.

Variable region sequence modulates periplasmic export of a single-chain Fv antibody fragment in Escherichia coli.

Using PCR, we have cloned antibody heavy and light chain variable region (VH and VL) coding sequences specific for a recombinant hepatitis B virus surface antigen (HBsAg) and assembled these for expression as single-chain Fv (scFv) fragments in Escherichia coli periplasm using the ompA signal peptide. The vectors also encoded N- or C-terminal His6 extensions to allow for the purification of the expressed proteins using immobilized metal affinity chromatography (IMAC). We found that the VH-linker-VL configuration of the scFv was not exported to the periplasm but remained associated with cellular insoluble material, from which it could be extracted, renatured to its active form by gentle dialysis and purified using IMAC. The molecular size of the scFv suggests that the ompA signal peptide was not processed. Based on previous reports, we hypothesized that the arginine in framework 1 (FR1) of the VH might interfere with translocation to the periplasm by means of the signal peptide. Because no arginines are present in FR1 of VL, we reversed the order of the V-regions in the scFv and observed efficient export of the active scFv to the periplasm. Furthermore, when the arginine in FR1 of VH was mutated to glycine in the original VH-linker-VL construct, active scFv was also exported to the periplasm. Thus, exposed positive charges near the signal peptide may account for at least some of the often-encountered difficulties in bacterial scFv expression.

Intra- and extracellular expression of an scFv antibody fragment in E. coli: effect of bacterial strains and pathway engineering using GroES/L chaperonins.

We have studied the influence of bacterial host on the secretion of single-chain Fv antibody fragment (scFv), the production of this antibody fragment as intracellular fusion protein, and the effect of chaperonin coexpression on intracellular antibody expression. Seven bacterial strains were transformed with a vector carrying the genes encoding the variable regions of an anti-CEA scFv antibody and the ompA leader sequence (ptrp/ompA/scFvCEA). Expression and secretion of this antibody fragment were highest in the W3110 strain, as determined by Western blot analysis and enzyme immunoassay, where the scFv fragment amounted to approximately 30% of the total periplasmic protein. Except for BMH71-18, the other strains were unsuitable for antibody fragment expression, suggesting screening of bacterial strains as an important parameter. For intracellular expression, the scFv was expressed as a fusion protein with a 26-amino acid N-terminal fragment of human interleukin-2 (IL-2), using the pIL-2f/scFvCEA vector. The fusion protein was expressed at 30% of total biomass and retained antigen binding after in vitro refolding. Co-expression of chaperonin-encoding plasmid pGroES/L with pIL-2f/scFv increased the intracellular production of the fusion protein twofold, with a similar increase in the final amount of active scFv antibody fragment that could be obtained after in vitro refolding. The chaperonins had no effect on secretion of scFv antibody fragments, using the ptrp/ompA/scFvCEA.

Purification and application of a single-chain Fv antibody fragment specific to hepatitis B virus surface antigen.

Immobilized metal affinity chromatography (IMAC) has been recently applied to the purification of of recombinant proteins bearing multi-histidine domains at their N or C terminus. We have now used this procedure for the single-step purification of an anti-Hepatitis B virus surface antigen (HBsAg) single-chain Fv (scFv) antibody fragment. Adjusting the metal ion (Cu+2 or Ni+2) and elution conditions (pH or imidazole), we efficiently separated active scFv forms from inactive molecules. Achieved purity was 93%, with a 20% yield with respect to the scFv content in the initial material. The pure scFv was coupled to CNBr-activated Sepharose 4B and compared the original monoclonal antibody (MAb) CB-Hep.1 in the immunoaffinity purification of a vaccine recombinant HBsAg (r-HBsAg). Results indicate that eluted antigen per mg of coupled ligand was similar for the scFv and the MAb when pure r-HBsAg was used as starting material. Preliminary results with unpurified starting material are also encouraging.

CEA in colonic adenocarcinomas and precancerous lesions. An immunohistochemical study with a novel monoclonal antibody.

Using a new anti-CEA (CB-CEA-1) murine monoclonal antibody, the expression of carcinoembryonic antigen (CEA) was studied in normal, premalignant and malignant human adult tissues with particular emphasis on colorectal mucosa. The CB-CEA-1 epitope was poorly expressed in normal adult tissues but was consistently found in colon cancers and adenomas in distinctive immunohistochemical patterns. Some apical staining was found with CB-CEA-1 in cells of normal colon mucosa whereas colon adenocarcinomas had a predominantly cytoplasmic staining pattern. Colonic adenomas presented a varied staining pattern. Some showed apical staining, others a CEA distribution pattern similar to that of adenocarcinomas, particularly those with a villous component. Our findings indicate a differential expression of CB-CEA-1 in adenoma cells in relation to their potential for malignant transformation. The possible usefulness of this Mab defined epitope for diagnostic and therapeutic purposes is indicated.

Hepatitis E virus in Cuba.

The hepatitis E virus (HEV) has a global distribution and is known to have caused large waterborne epidemics of icteric hepatitis. The transmission is primarily fecal-oral. Some reports have suggested parenteral transmission of HEV from its association to hepatitis B or hepatitis C infection, or due to the development of hepatitis E after blood transfusion. Though most of the developing countries in Asia and Africa have been shown to be endemic for HEV infection, studies in the Latin American countries have been limited to Mexico, Brazil and Venezuela. We have developed an enzyme immunoassay (EIA) for IgM and IgG antibodies to a recombinant protein containing antigenic epitopes of the ORF3 region of the HEV. This system, as well as a commercial kit that includes ORF2 and ORF3 antigenic epitopes, were used to study the prevalence of anti-HEV antibodies in a sample of Cuban blood donors, acute hepatitis cases and individuals subjected to plasmapheresis. The incidence of anti-HEV IgM was compared with other viral hepatitis markers. Our findings suggest that infections due to HEV are an important viral cause of sporadic hepatitis in Cuba, and that HEV is endemic to this region of the world.

A recombinant protein based immunoassay for the combined detection of antibodies to HIV-1, HIV-2 and HTLV-I.

The aim of this study was to develop and evaluate a combined assay for the detection of antibodies to HIV-1, HIV-2 and HTLV-I (human T-cell leukemia virus type I). A mixture of recombinant proteins and synthetic peptides was fixed to the surface of microELISA wells and a protein A peroxidase conjugate was used as tracer. The combined assay was compared to specific HIV-1/2 and HTLV-I commercial ELISAs. The sensitivity was studied with a panel of 158 HIV-1, 82 HIV-2 and 48 HTLV-I positive sera, all of which were reactive in the combined assay. The analytical sensitivity was studied with a panel of serially diluted sera and was similar to that obtained for the specific ELISAs. The specificity of the test was 99.78% against a panel of 466 negative sera collected from voluntary donors that included HBsAg, HCV, and VDRL positive sera. The false positive serum was borderline in the HTLV-I specific ELISA. The new combined ELISA can be used as an efficient initial screening assay, avoiding the cost of individual tests for HIV and HTLV.

A bacterial single-chain Fv antibody fragment that inhibits binding of its parental anti-E-selectin monoclonal antibody to activated human endothelial cells.

Using the polymerase chain reaction, we cloned, modified, and linked antibody variable (V) region coding genes from a mouse hybridoma, and produced a bacterial single-chain Fv (scFv) antibody fragment specific for E-Selectin. A vector of pBR322 origin, bearing the tryptophan promoter and the ompA bacterial signal peptide, was used to direct scFv expression to periplasm. The vector included a six-histidine coding sequence 5' to the scFv for the purification of the expressed protein using immobilized metal affinity chromatography (IMAC). We found that the VH-Linker-VL 32-33 kDa scFv remained insoluble after cellular fractionation, and transmission electron microscopy showed the new protein to be present in the periplasm as inclusion bodies. The scFv was solubilized using urea, purified using IMAC, and renatured to its active form. In a competitive enzyme-linked immunosorbent assay with activated human vein endothelial cells in the solid phase, the scFv competed for binding with the original monoclonal antibody.

High cytoplasmic expression in E. coli, purification, and in vitro refolding of a single chain Fv antibody fragment against the hepatitis B surface antigen.

A single-chain Fv (scFv) antibody fragment against the hepatitis B surface antigen (HBsAg) was expressed in Escherichia coli in the form of two independent fusion proteins, with either 60 ('long') or 27 ('short') amino acid N-terminal encoding sequences related to human interleukin-2. Both fusion proteins were expressed insolubly and at high levels in the bacterial cytoplasm (approximately 30% of total bacterial protein in MM294 cells at a laboratory scale). When recombinant cells were cultured in 5-1 fermentors, expression and optical density increased 2- and 4-fold, respectively, compared to a previous periplasmic insoluble version of the same anti HBsAg scFv. After extraction and solubilization in urea, the cytoplasmic scFvs were purified using immobilized metal ion affinity chromatography, followed by DTT treatment, and refolding by dialysis against a basic pH buffer containing EDTA. The refolded scFvs recognized the recombinant HBsAg in ELISA. Results of an ELISA where antigen affinity chromatography repurified scFvs were used as standards, indicated that refolding efficiencies were high: 56.2% for the 'short' fusion scFv, and 50.6% for the 'long' fusion scFv. Corrected final yields of active scFv were 30.3 and 27.3 mg l-1, respectively, for the aforementioned fusion proteins, 5-6 times better than those reported for the periplasmic scFv variant.

Very high expression of an anti-carcinoembryonic antigen single chain Fv antibody fragment in the yeast Pichia pastoris.

In this paper we report the development of a recombinant strain of the yeast Pichia pastoris, which secretes an anti-carcinoembryonic antigen single chain Fv (scFv) antibody fragment to the culture supernatant as a biologically active protein, at levels of 1.2 g l(-1). The yeast scFv was purified by IMAC, with a final yield of approximately 0.440 g of 93% pure scFv per liter of culture supernatant. The specific activity in ELISA of the yeast scFv was almost three times higher than that of a bacterial periplasmic counterpart. These results reaffirm that the yeast P. pastoris is a suitable host for high level production of scFv antibody fragments with potential in vivo diagnostic and therapeutic applications.

A simple visual immunoassay (VIA) for the semiquantitative determination of plasma elastase levels.

Elastase levels are an important marker of the extent and severity of inflammatory processes. We describe a visual immunoassay based on two monoclonal antibodies for the semi-quantitative determination of plasma elastase levels. The method is rapid, reliable, easy to perform, and does not require special laboratory equipment. There is coincidence of our results with those obtained by quantitative methods. The assay is suitable to obtain information for the management of patients in most intensive care units.

Hexa-histidine tag as a novel alternative for one-step direct labelling of a single-chain Fv antibody fragment with 99m Tc.

From genetic material of hybridoma cells, we have generated a recombinant single-chain antibody fragment (scFv antibody) specific to carcinoembryonic antigen (CEA), which can substitute an intact murine monoclonal immunoglobulin G1 (IgG1) antibody, also developed by our group, and used in clinical practice for many years. In this paper, we examine a novel one-step method for direct 99mTc labelling of a recombinant anti-CEA scFv fragment through a C-terminal peptide tag containing a six-histidine sequence. This C-terminal peptide tag does not affect antigen binding, and was employed as a strategy for the one-step method of direct 99mTc labelling of a recombinant antibody fragment, based on the criteria of Zamora and Rhodes (Zamora PO, Rhodes BA. Imidazoles as well as thiolates in proteins bind technetium-99m. Bioconj Chem 1992; 3: 493-498). This is a novel technique for the rapid labelling of molecules, suitable for in vivo trials. The method yields >95% labelling efficiency without major effects on biological or in vitro stability.

Monoclonal antibodies against the major coat protein of filamentous phage as a useful analytical tool for bacteriophage peptide/protein display.

Four mouse monoclonal antibodies (MAbs) that react with filamentous M13KO7 and R408 phage were obtained. Three of these MAbs (two IgG2a and one IgG3) recognize linear sequences of the p8 main structural coat protein, and one (IgG2a) identifies a putatively conformational epitope, as suggested by Western blot. These MAbs also react with recombinant phage expressing peptide antigens fused to p8, and are though useful reagents for peptide/protein phage display screening based methods. The latter was shown in an enzyme-linked immunoadsorbent assay (ELISA) and a visual immunoassay where one of the anti-p8 MAbs was used to capture recombinant phages displaying a peptide characteristic of the Hepatitis B virus surface antigen or a Dengue virus-related peptide antigen.

Specific active immunotherapy with a VEGF vaccine in patients with advanced solid tumors. results of the CENTAURO antigen dose escalation phase I clinical trial.

CIGB-247 is a novel cancer therapeutic vaccine that uses a human VEGF variant molecule as antigen, in combination with a bacterial adjuvant. In mice, CIGB-247 has anti-tumor and anti-metastatic effects. The vaccine induces anti-VEGF blocking antibodies and a cellular response targeting tumor cells producing VEGF, and has proven to be safe in mice, rats, rabbits and non-human primates. Herein we report the results of a Phase I clinical trial (code name CENTAURO) where safety, tolerance, and immunogenicity of CIGB-247 were studied in 30 patients with advanced solid tumors, at three antigen dose levels. Individuals were subcutaneously immunized for 8 consecutive weeks with 50, 100 or 400 µg of antigen, and re-immunized on week twelve. On week sixteen, evaluations of safety, tolerance, clinical status, and immunogenicity (seroconversion for anti-VEGF IgG, serum VEGF/KDR-Fc blocking ability, and gamma-IFN ELISPOT with blood cells stimulated in vitro with mutated VEGF) were done. Surviving patients were eligible for off-trial additional 4-week re-immunizations with 400 µg of antigen. Immunogenicity and clinical status were again studied on weeks 25 and 49. Vaccination was shown to be safe at the three dose levels, with only grade 1-2 adverse events. CIGB-247 was immunogenic and higher numbers of individuals positive to the three immune response tests were seen with increasing antigen dose. Off-protocol long-term vaccination produced no additional adverse events or negative changes in immunogenicity. Eleven patients are still alive, with overall survivals ranging from 20 to 24 months. Twelve of the thirty patients exhibited objective clinical benefits, and two individuals have complete responses. Most patients with higher survivals are positive in the three immune response tests. In summary, this is the first clinical testing report of a cancer therapeutic vaccine based on a human VEGF related molecule as antigen. The CIGB-247 vaccine is safe, immunogenic, and merits further clinical development. REGISTRATION NUMBER AND NAME OF TRIAL REGISTRY: RPCEC00000102. Cuban Public Clinical Trial Registry (WHO accepted Primary Registry). Available from: http://registroclinico.sld.cu/.

Displaying human interleukin-2 on the surface of bacteriophage.

Previous attempts to produce active human Interleukin-2 (hIL-2) in E. coli have failed, due to its aggregation in the form of cytoplasmic inclusion bodies, and the inability of the protein to enter the periplasmic export pathway, when fused to bacterial signal sequences. We have reasoned that these limitations could be overcome by introducing changes in the signal sequence and/or in some hIL-2 residues, not critical for its biological activity; and proceeded to test this hypothesis using a phagemid vector carrying the pelB secretion signal sequence, and the filamentous phage display system. Deletion of the Pro +2 in hIL-2 led to the export of a correct size (processed) molecule to the bacterial periplasm of Su- cells by the phagemid vector. However, this was achieved under growth conditions that would not favor phage assembly in Su+ strains. Changing the hydrophobic core of the leader peptide reversed this situation and allowed phage assembly and display of a pIII/hIL-2 hybrid protein in TG1 cells. The phage-displayed hIL-2 is correctly folded, as judged by its ability to interact with a conformation-specific anti-hIL-2 monoclonal antibody, and maintains its biological activity when tested in a CTLL-2 cell proliferation assay. The changes introduced in hIL-2 and the signal sequence will make possible to use the powerful phage display technology for the selection of high-affinity variants from libraries of hIL-2 mutants.

Production, purification and characterization of an anti-(carcinoembryonic antigen) recombinant single-chain Fv antibody fragment.

Specific targeting of radioactive agents to tumour cells has been the main objective of the in vivo use of monoclonal antibodies and their fragments. In particular, specific antibodies to carcinoembryonic antigen (CEA)-expressing tumours can be used either for diagnosis or therapy, if targeting could be improved. The expression of antibody fragments in bacteria allows the preparation of engineered molecules with antigen-binding properties and a better penetration into the tumour. A specific anti-CEA single-chain Fv fragment was produced in bacteria and purified. Its binding activity has been demonstrated in ELISA, immunocytochemistry, immunohistochemistry, fluorescence-activated cell sorting and the kinetic parameters determined by the plasmon surface resonance.

Production of active anti-CD6 mouse/human chimeric antibodies in the milk of transgenic mice.

The expression of chimeric genes in the mammary gland of transgenic farm animals has become an alternative for the large-scale production of recombinant proteins and for the modification of milk composition. In this paper, we show that a mouse/human chimeric antibody against the human CD6 leukocyte antigen can be assembled and correctly folded by the mammary gland, and secreted to milk, where it maintains its specificity. The base sequences encoding for the heavy and light chain variable regions of the anti-CD6 mouse monoclonal antibody IOR-T1 were cloned by the polymerase chain reaction from hybridoma cDNA, coupled to human heavy and light chain constant region genes, and inserted in a vector containing the 5' regulatory region of the rabbit whey acidic protein gene. Transgenic mice were produced by conventional pronuclei microinjection techniques. Integration and transgene copy number were determined by Southern blot. Assembled human immunoglobulin was detected in milk using a sandwich ELISA. Expression levels of chimeric antibodies in milk were determined to be around 400 micrograms/ml by Western blot, using CHO-derived chimeric IOR-T1 antibodies as reference. The chimeric antibodies produced in milk recognized human peripheral blood T lymphocytes by indirect immunofluorescence, with the classical patch-like pattern of IOR-T1.