A recombinant antigen-binding blocking protein against PD1 or antigen-binding blocking fragment thereof against PD1 comprising one of: an antigen binding region comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 32, SEQ ID NO: 53, a fragment thereof and a homologous sequence thereof; an antigen binding region comprising a variable light chain and variable heavy chain, respectively, with amino acid sequences selected from SEQ ID NOS: 28 and 30; SEQ ID NOS: 49 and 51, fragments thereof and homologous sequences thereof; an antigen binding region comprising: (i) a light chain comprising LCCDR1, LCCDR2 and LCCDR3 respectively, having the amino acid sequence SSNIGNNA (SEQ ID NO: 23), YND and AAWDDSVNGYV (SEQ ID NO: 24) and a heavy chain comprising HCCDR1, HCCDR2 and HCCDR3 respectively, having amino acid sequences GYTFTRFG (SEQ ID NO: 25), ISVNNGNT (SEQ ID NO. 26) and ARYMYGRRDS (SEQ ID NO: 27); fragments thereof and homologous sequences thereof; or (ii) a light chain comprising LCCDR1, LCCDR2 and LCCDR3 respectively, having the amino acid sequence NIGSKS (SEQ ID NO: 34), YDS and QVWDSSSDYV (SEQ ID NO: 45) and a heavy chain comprising HCCDR1, HCCDR2 and HCCDR3 respectively, having amino acid sequences GFTFSSYA (SEQ ID NO: 46), ISGSGGST (SEQ ID NO. 47) and ARNYISMFDS (SEQ ID NO: 48); fragments thereof and homologous sequences thereof; wherein said antigen-binding protein comprises a secretable scFv. an antigen binding region comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 32, SEQ ID NO: 53, a fragment thereof and a homologous sequence thereof; an antigen binding region comprising a variable light chain and variable heavy chain, respectively, with amino acid sequences selected from SEQ ID NOS: 28 and 30; SEQ ID NOS: 49 and 51, fragments thereof and homologous sequences thereof; an antigen binding region comprising: (i) a light chain comprising LCCDR1, LCCDR2 and LCCDR3 respectively, having the amino acid sequence SSNIGNNA (SEQ ID NO: 23), YND and AAWDDSVNGYV (SEQ ID NO: 24) and a heavy chain comprising HCCDR1, HCCDR2 and HCCDR3 respectively, having amino acid sequences GYTFTRFG (SEQ ID NO: 25), ISVNNGNT (SEQ ID NO. 26) and ARYMYGRRDS (SEQ ID NO: 27); fragments thereof and homologous sequences thereof; or (ii) a light chain comprising LCCDR1, LCCDR2 and LCCDR3 respectively, having the amino acid sequence NIGSKS (SEQ ID NO: 34), YDS and QVWDSSSDYV (SEQ ID NO: 45) and a heavy chain comprising HCCDR1, HCCDR2 and HCCDR3 respectively, having amino acid sequences GFTFSSYA (SEQ ID NO: 46), ISGSGGST (SEQ ID NO. 47) and ARNYISMFDS (SEQ ID NO: 48); fragments thereof and homologous sequences thereof; wherein said antigen-binding protein comprises a secretable scFv. (i) a light chain comprising LCCDR1, LCCDR2 and LCCDR3 respectively, having the amino acid sequence SSNIGNNA (SEQ ID NO: 23), YND and AAWDDSVNGYV (SEQ ID NO: 24) and a heavy chain comprising HCCDR1, HCCDR2 and HCCDR3 respectively, having amino acid sequences GYTFTRFG (SEQ ID NO: 25), ISVNNGNT (SEQ ID NO. 26) and ARYMYGRRDS (SEQ ID NO: 27); fragments thereof and homologous sequences thereof; or (ii) a light chain comprising LCCDR1, LCCDR2 and LCCDR3 respectively, having the amino acid sequence NIGSKS (SEQ ID NO: 34), YDS and QVWDSSSDYV (SEQ ID NO: 45) and a heavy chain comprising HCCDR1, HCCDR2 and HCCDR3 respectively, having amino acid sequences GFTFSSYA (SEQ ID NO: 46), ISGSGGST (SEQ ID NO. 47) and ARNYISMFDS (SEQ ID NO: 48); fragments thereof and homologous sequences thereof;