VTCN1 (V-set Domain Containing T-cell Activation Inhibitor 1, VCTN1, B7H4, B7-H4, B7h.5, B7S1, B7X, FLJ22418, Immune Costimulatory Protein B7-H4, PRO1291, Protein B7S1, RP11-229A19.4, T-cell Costimulatory Molecule B7x, UNQ659) Antibody