Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the treatments for Progressive Multifocal Leukoencephalopathy ?
    ### Response:
    Currently, the best available therapy is reversal of the immune-deficient state, since there are no effective drugs that block virus infection without toxicity. Reversal may be achieved by using plasma exchange to accelerate the removal of the therapeutic agents that put patients at risk for PML.
    