31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Efficient immunoglobulin gene disruption and targeted replacement in rabbit using zinc finger nucleases.

Rabbits are widely used in biomedical research, yet techniques for their precise genetic modification are lacking. We demonstrate that zinc finger nucleases (ZFNs) introduced into fertilized oocytes can inactivate a chosen gene by mutagenesis and also mediate precise homologous recombination with a DNA gene-targeting vector to achieve the first gene knockout and targeted sequence replacement in rabbits. Two ZFN pairs were designed that target the rabbit immunoglobulin M (IgM) locus within exons 1 and 2. ZFN mRNAs were microinjected into pronuclear stage fertilized oocytes. Founder animals carrying distinct mutated IgM alleles were identified and bred to produce offspring. Functional knockout of the immunoglobulin heavy chain locus was confirmed by serum IgM and IgG deficiency and lack of IgM(+) and IgG(+) B lymphocytes. We then tested whether ZFN expression would enable efficient targeted sequence replacement in rabbit oocytes. ZFN mRNA was co-injected with a linear DNA vector designed to replace exon 1 of the IgM locus with ∼1.9 kb of novel sequence. Double strand break induced targeted replacement occurred in up to 17% of embryos and in 18% of fetuses analyzed. Two major goals have been achieved. First, inactivation of the endogenous IgM locus, which is an essential step for the production of therapeutic human polyclonal antibodies in the rabbit. Second, establishing efficient targeted gene manipulation and homologous recombination in a refractory animal species. ZFN mediated genetic engineering in the rabbit and other mammals opens new avenues of experimentation in immunology and many other research fields

Functionality and sequence diversity of the recombinant antibodies per animals and bleeds.

*<p>”Functional” refers to the biochemical IL1RL1:IL33 inhibition assay with a cut off of ≥40% inhibition.</p

Concordance of VL and VH sequences of single <i>E. coli</i> colonies derived from pool-cloning shown for 8 different B-cell clones (ASCs).

<p>Concordance of VL and VH sequences of single <i>E. coli</i> colonies derived from pool-cloning shown for 8 different B-cell clones (ASCs).</p

A Robust High Throughput Platform to Generate Functional Recombinant Monoclonal Antibodies Using Rabbit B Cells from Peripheral Blood

<div><p>We have developed a robust platform to generate and functionally characterize rabbit-derived antibodies using B cells from peripheral blood. The rapid high throughput procedure generates a diverse set of antibodies, yet requires only few animals to be immunized without the need to sacrifice them. The workflow includes (i) the identification and isolation of single B cells from rabbit blood expressing IgG antibodies, (ii) an elaborate short term B-cell cultivation to produce sufficient monoclonal antigen specific IgG for comprehensive phenotype screens, (iii) the isolation of VH and VL coding regions via PCR from B-cell clones producing antigen specific and functional antibodies followed by the sequence determination, and (iv) the recombinant expression and purification of IgG antibodies. The fully integrated and to a large degree automated platform (demonstrated in this paper using IL1RL1 immunized rabbits) yielded clonal and very diverse IL1RL1-specific and functional IL1RL1-inhibiting rabbit antibodies. These functional IgGs from individual animals were obtained at a short time range after immunization and could be identified already during primary screening, thus substantially lowering the workload for the subsequent B-cell PCR workflow. Early availability of sequence information permits one to select early-on function- and sequence-diverse antibodies for further characterization. In summary, this powerful technology platform has proven to be an efficient and robust method for the rapid generation of antigen specific and functional monoclonal rabbit antibodies without sacrificing the immunized animal.</p></div

Yield of IL1RL1-specific rabbit antibodies.

<p>Scatter Plots depicting the yield of the primary screening using all 7644 supernatants: (<b>A</b>) Human IL1RL1 binding (unit: optical density (OD)) versus IgG concentration; (<b>B</b>) human IL1RL1 binding versus cynomolgus IL1RL1 binding or versus (<b>C</b>) murine IL1RL1 binding. Scatter Plot showing the correlation of the biochemical inhibition assay with the cellular inhibition assay: (<b>D</b>) Threshold ≥40% inhibition, RSq: 0.36, (<b>E</b>) magnification of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086184#pone-0086184-g003" target="_blank">Figure 3D</a> using the threshold of >90% inhibition, RSq: 0.9. The statistically confirmed cut off values for the calculation of the percentages were as follows: rabbit IgG-positive >0.013 µg/ml, human IL1RL1-positive >OD 0.195, human Fc-positive ≤OD 0.125, cynomolgus IL1RL1-positive >OD 0.184, murine IL1RL1-positive >OD 0.164. Green are the supernatants deriving from the pre-incubation only scenario and red are the SN after the protein panning step. The diamond, the circle and the cross indicate the three different animals. (<b>F</b>) Result of the two dimensional binding matrix identifying different binding epitopes on human IL1RL1. The colored numbers indicate different antigen specific antibodies. The black numbers describe the three antibody groups. The degree of antibody competition in the matrix is depicted by a 3-colour scale with green, black, red color indicating highest competition, mid or lowest competition, respectively.</p

Analysis of the VH-VDJ and VK-VJ sequences to assess clonality and diversity of the recombinant rabbit antibodies.

<p>The distribution of the (A) CDR-H3 length (amino acid count) and of the (B) amino acid replacement frequency within the VH region in comparison to VHa1 and VHa3 allotype germ line sequences. Dark grey: VH1a1 germ line gene; light grey: VH1a3 germ line gene. (C) Clustering of the rabbit antibodies according to their CDR-H3 and CDR-L3 sequence similarity. The bold numbers indicate the rabbits.</p

Influence of the improvements of the B-cell handling and the B-cell cultivation.

<p>(<b>A</b>) Percentage of IgG-producing B-cell clones per total wells and (<b>B</b>) average IgG concentration over all IgG-positive wells after +/− pre-incubation in medium and +/− centrifugation post sorting. For each parameter 368 wells were analyzed. (<b>C</b>) Percentage of IgG-producing B-cell clones (ASCs) per total wells and (<b>D</b>) average IgG concentration over all IgG-positive wells after using +/− SAC in a dilution of 1∶20000 during B-cell cultivation. For each parameter 252 wells were analyzed. (<b>E</b>) Percentage of IgG-producing B-cell clones per total wells, (<b>F</b>) average IgG concentration over all IgG-positive wells, as well as percentage of antigen specific B-cell clones (<b>G</b>) per total wells and (<b>H</b>) per IgG-producing B-cell clones after +/− protein panning. For each parameter around 3500 wells were analyzed. The error bars represent the standard deviation. The cut off value of IgG-positive wells was >0.013 µg/ml IgG and of human IL1RL1-positive wells was>OD 0.195.</p