Method for cancer immunotherapy

1. An isolated antibody which binds to the compound of formula (1):

wherein X is a tyrosine residue or a methionine residue; each of Y and Z is independently a single bond,

R 1 is hydrogen or alkyl,

R 2 is hydroxyl, amino, alkylamino or dialkylamino,

R 3 is hydrogen, alkyl, amino, alkylamino, dialkylamino or substituted or unsubstituted alkylcarbonylamino,

R 4 is hydrogen, alkyl, carboxy, carbamoyl, alkylcarbamoyl, dialkylcarbamoyl or a group of formula (2):

wherein W is an amino acid residue,

m is 1 or 2, and

n is an integer of 0-2, with the proviso that when n is 0, R 3 is hydrogen or alkyl, or a pharmaceutically acceptable salt thereof.

2. The isolated antibody of claim 1 , which binds to the compound of formula (4):

or a pharmaceutically acceptable salt thereof.

3. The isolated antibody of claim 1 , which binds to the compound of formula (5):

or a pharmaceutically acceptable salt thereof.

4. A monoclonal antibody which binds to the compound of formula (1):

wherein X is a tyrosine residue or a methionine residue; each of Y and Z is independently a single bond,

R 1 is hydrogen or alkyl,

R 2 is hydroxyl, amino, alkylamino or dialkylamino,

R 3 is hydrogen, alkyl, amino, alkylamino, dialkylamino or substituted or unsubstituted alkylcarbonylamino,

R 4 is hydrogen, alkyl, carboxy, carbamoyl, alkylcarbamoyl, dialkylcarbamoyl or a group of formula (2):

wherein W is an amino acid residue,

m is 1 or 2, and

n is an integer of 0-2, with the proviso that when n is 0, R 3 is hydrogen or alkyl, or a pharmaceutically acceptable salt thereof.

5. The monoclonal antibody of claim 4 , which binds to the compound of formula (4):

or a pharmaceutically acceptable salt thereof.

6. The monoclonal antibody of claim 4 , which binds to the compound of formula (5):

or a pharmaceutically acceptable salt thereof.