Here are some excerpts from the Secret Doctrine by H.P.Blavatsky about the Book of Dzyan inter alia.
The Teshu Lama and the Panchen Lama appear to be the same being.
The successive Panchen Lamas form a tulku reincarnation lineage which are said to be the incarnations of Amitābha. The title, meaning “Great Scholar”, is a Tibetan contraction of the Sanskrit paṇḍita (scholar) and the Tibetan chenpo (great). The Panchen Lama traditionally lived in Tashilhunpo Monastery in Shigatse. From the name of this monastery, the Europeans referred to the Panchen Lama as the Tashi-Lama (or spelled Tesho-Lama or Teshu-Lama).
Other titles of Panchen Lama include “Panchen Bogd“, the original title given by Altan Khan at the creation of the lineage. “Bogd” (Mongolian: ᠪᠣᠭᠳᠠ богд) is Mongolian, meaning “holy, saint”. In 1713, 5th Panchen Lama Lobsang Yeshe received the title “Panchen Erdeni” from Kangxi Emperor of Qing Empire, which is inherited by successive Panchen Lamas since then. “Erdeni”, or “Erdini”, (Manchu: ᡝᡵᡩᡝᠨᡳ erdeni) is Manchu, meaning “treasure”.