Case series of the first three severe COVID-19 patients treated with the secretome of hypoxia-mesenchymal stem cells in Indonesia [version 3; peer review: 2 approved] oleh Basuki Rachmad, Flora Eka Sari, Fajar Amansyah, Sugeng Ibrahim, Agus Widyatmoko, Agung Putra, Zenitalia Pasongka, Retnaningsih Retnaningsih, Mukti Arja Berlian, Farid Amansyah