TB (Transport Block) is associated with the MAC layer. MAC layer sends the data in the form of transport block. HARQ is MAC layer functionality and maximum HARQ is reached then in that case RLC layer starts ARQ procedure for AM entity. When ARQ procedure starts, the data re-transmission again re-starts. For the MAC layer again it is a data and HARQ procedure gets applicable.
In essence, upper layer RLC decides whether re-transmission is required or not. Based on that re-transmission of RLC PDU starts.
