The invention provides a method of obtaining a population of antigen-specific T cells comprising: (i) dividing PBMCs from peripheral blood of a host into more than one sub-population； (ii) contacting the PBMCs of each sub-population with an antigen； (iii) obtaining a sample of the contacted PBMCs from each sub-population； (iv) measuring the quantity of 1) IL-2 mRNA and 2) IFN-γ mRNA expressed by the PBMCs of each sample； (v) determining the IL-2 index of each sample； (vi) identifying one or more samples with an IL-2 index determined in (v) of greater than or equal to about 10 to identify one or more antigen-reactive, central memory T cell sub-populations； (vii) dividing the antigen-reactive, central memory T cell sub-population(s) identified in (vi) into microcultures； (viii) identifying one or more antigen-reactive microcultures； and (ix) expanding the microculture(s).
