Simultaneous transfer of delayed hypersensitivity to diphtheria toxin and to tuberculin has been accomplished in eight consecutive instances in man using extracts from washed leucocytes taken from the peripheral blood of tuberculin-positive, Schick-negative donors who were highly sensitive (i.e., pseudoreactors) to purified diphtheria toxin and toxoid. The leucocyte extracts used for transfer contained no detectable antitoxin. The recipient subjects were Schick-positive (<0.001 unit antitoxin per ml. serum) and tuberculin-negative at the time of transfer. All the recipients remained Schick-positive for at least 2 weeks following transfer and in every case their serum contained less than 0.001 units antitoxin at the time when they exhibited maximal skin reactivity to toxoid.

Evidence is presented which indicates that the transfer factor may be released from leucocyte suspensions under mild conditions in which most of the cells appear to remain morphologically intact.

Four adult Schick-positive subjects have been sensitized to diphtheria toxoid by intradermal injection of a few micrograms of purified toxoid in the form of a washed toxoid-antitoxin precipitate. Two of these sensitized individuals showed severe delayed skin reactions specifically directed against diphtheria toxin (or toxoid) at a time when their serum antitoxin level was less than 0.001 units/ml.

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