Proteolytic digestion of the cyclic adenosine monophosphate (cAMP) receptor protein (CRP) in the presence of cAMP results in the formation of a resistant core molecule. The CRP core retains the dimeric structure and cAMPbinding properties of the native CRP, while cAMP-dependent DNA binding is lost. CRP consists of two identical polypeptides of molecular weight 22 500. The CRP cores formed after proteolytic digestion in the presence of 0.1 mM cAMP differ in molecular weight: subtilisin and trypsin CRP cores, ~12 500; chymotrypsin CRP core, ~13 000; and Straphylococcus V8 protease CRP core, ~18 000. In the absence of cAMP, CRP is relatively resistant to these enzymes. The aCRP core produced by subtilisin digestion has been characterized as follows: The sedimentation coefficient of the aCRP 1 ranscription of catabolite-repressible operons involves the cAMP-dependent binding of CRP' to a site within the promoter of these operons (Pastan and Adhya, 1976). Proteolysis of the cyclic AMP receptor protein (CRP) in the presence of cAMP produces the a core fragment (aCRP) whose subunit of ~12 500 molecular weight is derived from the native CRP subunit of 22 500 molecular weight (Krakow and Pastan, 1973). While the CRP shows cAMP binding and cAMPdependent DNA binding at pH 8, the a core does not show this activity at pH 8, although its cAMP binding activity is retained. We have previously shown that cAMP produces a conformational change in the a core, resulting in an increased resistance to proteolysis and denaturation (Eilen and Krakow, 1977a). This event, in the native CRP, has been postulated to function as a conformational signal in effecting the formation of the DNA-binding site in the /3 region of the protein (Eilen f From the

Oncolytic viruses represent a promising form of cancer immunotherapy. We investigated the potential of Sindbis virus (SV) for the treatment of solid tumors expressing the human cancer testis antigen NYESO-1. NYESO-1 is an immunogenic antigen frequently expressed in numerous cancers, such as ovarian cancer. We show that SV expressing the tumor-associated antigen NYESO-1 (SV-NYESO1) acts as an immunostimulatory agent, inducing systemic and rapid lymphocyte activation, leading to a pro-inflammatory environment. SV-NYESO1 treatment combined with anti-programmed death 1 (anti-PD-1) markedly augmented the anti-tumor immunity in mice over the course of treatment, resulting in an avid systemic and intratumoral immune response. This response involved reduced presence of granulocytic myeloid-derived suppressor cells in tumors and an increase in the activation of splenic and tumor-infiltrating T cells. Combined therapy also induced enhanced cytotoxic activity of T cells against NYESO-1-expressing tumors. These results were in line with an observed inverse correlation between T cell activation and tumor growth. Finally, we show that combined therapy resulted in complete clearance of NYESO-1-expressing tumors in vivo and led to long-term protection against recurrences. These findings provide a rationale for clinical studies of SV-NYESO1 combined with immune checkpoint blockade anti-PD-1 to be used in the treatment of NYESO-1-expressing tumors.

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