PD-1 inhibitor （Pembrolizumab, 2mg/kg weight, once per 4 weeks and 3 times of medication usage）treatment on AIDS patients with progressive multifocal leukoencephalopathy.

This is a one-center, single-arm and prospective study, planing recruiting 10 AIDS-associated PML patients. All patients will receive PD-1 inhibitor (Pembrolizumab) for 12 weeks, and the dose for each time is 2 mg per kg/weight, and the frequency is once per 4 weeks. The effect and safety of Pembrolizumab on AIDS-associated PML will be evaluated.

Inclusion Criteria:

1. Age: 18-65
2. Diagnosed of HIV by lab confirmation
3. Diagnosed of PML by diplomatic radiologists through brain MRI or by brain biopsy once there are some concerns on radiologic diagnosis.
4. agree to sign the consent
5. agree to use contraception measures during 4 weeks before to 6 months after this study

Exclusion Criteria:

1. Pregnancy or lactating women or planing birth during this study
2. Anticipated bad treatment compliance
3. Within 6 months before joining this study, receive other immunosuppressors, immunomodulators or cytotoxic drugs (glucocorticoid is allowed)；
4. With neutrophil<1000/mm3 or platelet<75000/mm3 or allergic to PD-1 inhibitor 5）With severe basic diseases in heart, brain, lung, liver, kidney

6) disagree to sign the consent